Depending on the army, the place, the time and the supply situation, this could vary significantly.

Normally, all soldiers had a daily ration - some of it was delivered directly to the soldier to be put in his breadsack and be eaten as he pleased (cigarettes, chocolate, bread at times tinned food such as vegetables and meat).

Normally, food was distributed through the quartermaster's organisation down to the companies where field kitchens would cook the food for the troops. There were also field bakeries, field butcheries and many other supply organisations.

If at a quiet sector or in reserve, the troops of the platoons of the company would line up to get their food. If at the front, they would send a soldier as a runner to pick up a backpack-sized canteed to bring the food to the troops in the trenches.

The officers knew that the men could take more punishment, both physical and mental, if they got at least one hot meal per day and great efforts were made to bring hot food to the troops regardless of the supply or front situation.

Of course, this was not always possible, and hot food cooked at the field kitchen could be replaced by tinned food. Corned beef and spam were both common among the Western Allies. If possible, rifle squads would group together, combine their tinned food and heat it over a fire.

The British would cut old jerry cans (gasoline cans) in two and use gasline to heat them, fill them with water, condensed milk, sugar and tea to have hot tea every evening. Likewise they would pool their tinned food and make a hot meal.

Field kitchens tried to make food that was easy to eat, contained all you needed and was as palatable as possible. Food such as goulash (Hungarian meat stew with pepper, often with potatoes and vegetables added), stew, peasoup, meat soup and similar dishes were common. Field kitches were often referred to as gulaschkanone, goulash cannon due to the similarity of the stovepipe/chimney to a gun barrel.

Other food provided when hot food was not available was often cheese, small amounts of alcohol (often intended to be mixed with the water), chocolate, smoked or otherwise cured meat or saucages, dried fruits, bread and other foods that had a high calory density and lasted a long time without cooling.

To answer your questions.

1. Great efforts were made to supply the troops by all sides. Each unit had its own organisation with its own trucks, carts, cars, field kitchens etc to provide the troops both with hot and cold food. Most troops would have at least one hot meal per day most days.

2. A soldier would carry personal rations if going to the frontline, usually for a day or two. Runners would be sent back to the compamy supply depot for more or even hot food for the frontline troops if needed.

3. Yes, trains, then trucks (or horsecarts), then cooked at the field kitchen and then the troops either got ot the field kitchens, or runners got the food out to the troops. One notable difference in the Finnish Winter War was that the Finns managed to provide their troops with hot food much more often than the Soviets were, and Finnish troops had a better stamina and much better morale as a result.

4. People far from their supply depot would carry tinned food and cook it together if possible, else they would eat it cold.

5. If out of food, the troops would send runners back to the closest supply depot to bring tinned food or personal supplies of bread and dreid and curated food to the troops.

The Imperial Japanese Army's formal regulations prescribed a ration of primarily rice, along with barley (to deal with beriberi in the Pacific), some meat, vegetables, soy sauce, miso, and some sweets, theoretically producing a ration outcome of over 3,000 calories per day. In practice, the rapid pace of the Japanese advance, combined with the terrible Japanese logistics, resulted in soldiers being required to forage to complement their dietary needs. Sake was also available on occasion although it was not part of a combat ration.

You can take a look at the 1944 US War Department Intelligence Bulleting, which shows some nice pictures of Japanese Army food products.

Lots of different questions so i'm going to try and put them in order as best as possible. Sorry for the long answer in advance

Q1- amount of food carried- dependent upon tactical circumstances. most Soldiers would carry approx. 24-36 hours worth of food and water, exceptions generally being airborne, raiding and commando forces, who were generally expected to carry more (dependent upon tactical situation).

Q2- what did they eat- here is the British army's/Commonwealth's ration pack from WW2 http://reprorations.com/Britain%20WW2/WW2-Britain.htm note that regional variations did occur, for example the 'spam like product' was generally relabelled as 'meat' in India/Burma due to religious sensibilities complicating supply. The rations did suffer from an inability to 'lock in' vitamins and minerals, and getting the troops off rations was important to their health. The British army generally aimed at providing a meal from the field kitchens to the blokes about once a week or so, good for morale as much as their health. It should be appreciated however that this was dependent upon tactical situations, and other armies at the time generally did not place as high a emphasis upon such methods of man-management as the British army did.

Q3- How do they get resupplied- the western allies where entirely motorised by 1942 and consequently resupply was carried out by a combination of civilian or military railroads then off loading onto military trucks. Once those trucks have reached the frontlines they'll be offloaded onto smaller vehicles such as jeeps or the British Bren gun carrier and moved forwards under the supervision of the warrant officers and senior NCO cadre- resupply being the responsibility of Regimental and company sergeant majors.

Q4- Looting- dependent upon the Army and the level of discipline of that force, looting variety from a very minor issue to fully encouraged. Most soldiers hunted local game (if available) to improve generally monotonous rations (look over the British ration pack again with the mind-set that you'll be eating that for 6 weeks straight). Other food items must be simply be stolen or bought from the local population (D-Day Invasion forces were provided with francs, which they often used to purchase eggs, milk and meat from the local population, and alcohol when their officers weren't looking)

Q4- I'm just going to lump most of second part of your second paragraph into Difficultly- Hugely difficult to almost impossible, consider, for example D-Day if you are a logistics staff officer. you are responsible for finding the means of feeing, watering and resupplying with all manner of military materials to an initial force of 300,000 men, as they are moved 60- 100 miles in a night. your responsibilities are now not just resupplying that force, but thinking about how that force will grow, how your are going to sustain the advance inlands (a significant source of military academic anger regarding the 'phase lines' controversy) and also how you are going to resupply the resupply force. in the weeks before the Second Battle of El Alamein, Rommel's supply lines were 1,000 miles long, and it took 2 trucks full of petrol to get just 1 truck of petrol to the front. I would like to approach this question in more general terms, as food resupply was carried out by the same systems handled that ammunition, water and material resupply.

'Experience had taught it the penalties of neglecting logistical preparations, the germans, by contrast, accorded far less effort to logistical preparatinos because they were habituated to fighting continental wars across short distances supported by good communications. British generals, and in particular Montgomery, have been frequently castigated because of their habit of waiting until their logistical arrangement were in perfect order before taking the offensive. German generals, and in particular Rommel, have conversely been accorded high praise for their willingness to take risks with their logistics. these criticism fly in the face of all logic. The German system worked well across the short distances involved in fighting in France and Poland, and against enemies with an inferior operation doctrine....but in Russia, North Africa and finally in Normandy the German effort foundered, this was because their reach exceeded their logistical grasp. time and again in North Africa Rommel was able to achieve tactical successes, but lack of transport meant he could not transform them into operational victories. British offensives may have proceeded at a more stately pace, and on occasion the logistical system could not meet all demands placed upon it. But after 1941, major british operations rarely failed because of a breakdown of logistics'

French, D., Raising Churchill's army (Oxford, Oxford University press, 2000), p120-121

USA

Here's a good page about the types.

Basically they carried 1 days worth of rations. 3 M 'meat' types (meat and beans/rice/veggies different combos) 3 B 'bread' types ( biscuits/cereal also your candy/sugar/coffee and so on ) and you got an Accessory pack which had your cigarettes/ toilet paper/ chewing gum etc.

It's basically the same thing as a modern MRE minus the cigarettes and plus the tobasco sauce.

Also when in the field they may not have necessarily eaten C rations supplies would be brought from the rear for them to make which was basically the same stuff in the C-rations but in Big cans with sacks of flour and so on.

Then there's the stealing of food and trading with soldiers from other countries and taking it off a dead jerry or vice versa.

Bonus

There are specific packing instructions to load your haversack with and without your C-rations.

And i know this is frowned upon but if i was to venture a guess about how it was supplied.. There were constant flow of ships going back and forth be it military or merchant that were taking supplies to the different theaters and it was the first big war with good vehicles and i'd say as long as you weren't cut off from the closest base it wasn't too hard to get food delivered or have a soldier leg it back to the closest base and bring it back. But take this last party with a grain of salt.

Of all the times I'd want to dig up that WW2 picture book I had from when I was a kid.

First, context is going to be everything. A well supplied US camp in the middle of France in early '45 is going to be eating far better than one during the Bulge. The particulars would vary from country to country (British might have tins of tea, the Japanese would work with rice, the US were quite famous for their proto-spam canned meat products). The documentary "Soviet Storm" gives an idea of just how bad eating conditions could get- in Leningrad I think the ration of food at it's worst dropped to 200, 250 calories a day per person. And you'd only get it if you worked, most likely expending a bit more than that in the process.

A simple Google image search for "WW2 rations" gives you this- https://www.google.com/search?q=WW2+rations&source=lnms&tbm=isch&sa=X&ei=6x9hU6qkDcmayAT97oGQCQ&ved=0CAYQ_AUoAQ&biw=1920&bih=962#imgdii=_ which can help give you an idea of what they were eating. Some of the photos actually direct you to decent articles. While soldiers wouldn't look a prize horse in the mouth if they could hunt wild animals- or whatever happened to still be alive, like a stray cow, maybe they'll find some cellar with preserved veggies in it, or something fresh in the ground- typically their food consisted of whatever had a long shelf life. But at the same time, it couldn't be something that'd just as easily make them sick- starving soldiers won't fight well but neither will ones that are either constipated, or dehydrated because all their food is preserved in salt. Similarly, if they got no salt, that in itself was a huge problem. Furthermore there's a massive logistical effort to be carried out- soldiers might carry enough food for 2-4 days, depending on their unit (admittedly I think airmen only had the barest of survival rations carried in their aircraft, so I guess you could say 1-4?) and how much they'd ration it.

Cooking might be an art, but feeding an army is a science.

Here's a collection of some German ration items from the war- http://www.hitlersnest.co.uk/ww2%20german%20rations.htm

Here's some take-away from a quartermaster's presentation to their head in '49 (http://www.qmfound.com/history_of_rations.htm)

So they might not eat fresh food often, but they'd get their basic food groups. Quality protein was as important as carbohydrates. One of the biggest contributions the US made to the Soviet war effort was ironically canned meat (along with other food stuffs). Soldiers who don't get protein don't fight very well, and one of the first things the Germans did was blast through the Soviet bread basket of Ukraine and the surrounding area. I saw the actual figures somewhere else, I'll have to see if I can find it again. By some estimates the US sent enough food to the Union to feed 12,000,000 soldiers 1/2 pound of food every day for the duration of the war. Domestically provided foodstuffs typically included very simple things like a type of cabbage soup, boiled buckwheat (bread and butter food for the average Soviet citizen at the time) along with some odd combination of coffee (or tea), salt, bread, simple pasta noodles, and salted fish. Lend / Lease gave them spam, powdered egg, beans, dried peas, Tushonka (I can't find the source for where this was made, it could actually be soviet, but it was basically pork in gelatine. Yikes.) oil, butter, shortening, canned and dried milk, and grits. Sausage and bread was a very common staple for the Union soldiers because of it's longer shelf life with minimal preservation.

Outside of what was immediately carried on their person, soldiers also had the benefit in more ideal times of field kitchens. To give you an idea-

http://s642.photobucket.com/user/completearmourmodelling/media/35__cf.jpg.html

https://www.ww2incolor.com/d/116798-4/DZWI-RC_48-49_8%23

http://history.amedd.army.mil/ancwebsite/a&i/ww2-kw/w_13_62_45.JPG

Basically the idea was either something wheeled and carted by a motorized vehicle (horse, train. I don't think anyone devised an airdropped field kitchen, but food supplies could be airlifted), or something that was still easy to pack and move, that'd follow behind the soldiers, and give them properly cooked food.

Some armies had a ration of alcohol. While I can't find anything in the western allies, I know the Soviets rationed soldiers 100 grams of vodka, and the Germans rations beer to their soldiers.

This blog has some decent commentary on field eating conditions once you side step the politics- http://benandbawbsblog.blogspot.com/2010/10/lost-art-of-field-cooking-ii-field.html