Did they mostly survive on bread, or were other things commonly eaten? Was it common for troops to have a small amount of wine or other forms of alcohol on their person?
Oh fun question! Good news, actually - I've answered this question before! I'll go ahead and copy/paste here for convenience, but the original thread has some fun stuff in it. Like bacon recipes.
Starting off, the food ration of the Roman legions was pretty standard fare, and literary sources suggest that it consisted of grain (generally wheat - barley and oats were for the animals, unless you were decimated), meat (For some STRANGE reason, bacon was huge to their diet), cheese, vegetables (notably lentils), and a sour wine (called acetum - as opposed to the proper, vintage wine, which was known as vinum). There were no mess halls in the camp, so rations were issued to each soldier individually, and they would group together with their contubernium (tent-mates) to cook it in ovens that were made for that purpose. As a Roman legionary, you ate two meals a day - prandium (breakfast), and cena (supper). You also had to hope that you had a good cook in your contubernium ;)
Generally, the grain ration was issued in its basic form, though if you were on campaign, you got hardtack (lucky you!). The army had hand mills to grind the grain ration, and if you got the chance, you'd probably want to grind your hardtack down too, to turn it into flour. With that grain, you could make bread (The army had bakers), porridge (This one's for your friend!) or soup (remember the bacon and veggies? That actually doesn't sound half bad! Bacon and dumplings anyone?), or even into pasta. Yeah, the Romans had pasta.
One thing to note is that the meat ration DID depend a lot on what meat was local - if there were more sheep, then they ate mutton. More pigs? Pork and bacon. Cows? Steak tonight, baby! You understand ;) But the Romans DID have a pretty balanced diet. If they were a garrison or officers, there's a good chance that they would also augment the rations with local produce - we have records from the Wadi Fawakhir that mention bread, barley, oil, onions, radishes, cabbages, salted fish, decent wine, and meat. If you got paid more, you could augment that with oysters, sauces, spices, and fine wines. One "shopping list" that we have gives instructions to purchase:
"bruised beans, two modii [30.8 pints], chickens, twenty, a hundred apples, if you can find nice ones, one hundred or two hundred eggs, if they are for sale at a fair price, 8 sextarii [7.7 pints] of garum [a fish sauce that the Romans LOVED], a modius of olives..."
You get the idea :D Hope that answered your question, and if you have any more, please, feel free to ask!
Amazingly good answers to all questions! And superb references.
The legionaries were issued a ration of salt, which is the origin of both the English word 'salary' and the expression 'he isn't worth his salt.' Can't remember where I know this from.