It's a little complicated, since it's hard to understand the goals of rationing without context. I've written before on the background of why rationing in the United States became necessary, along with a little bit more on how it was implemented here and here.

The takeaway from this that I'd have you keep in mind for your question on allotments are that while unlike almost any participant in the war, the United States was generally self sufficient in most areas. However, there was massively increased demand given the economic boom that among other things eventually ended up increasing domestic meat consumption by a third during the war. It also had obligations to export significant quantities of food, especially proteins and fats, to its allies.

Add in that some of the things it actually was short in thanks to U Boat operations in the Caribbean and Japanese occupation in the Pacific - most notably sugar and cooking oils - and you can start seeing where unlimited choice and consumption became a problem.

So the first step is to both control inflation both for consumers and for military purchases, along with preventing shortages for both. In January 1942, the newly created Office of Price Administration is tasked with this and become alarmed at consumer prices rising at 14% and wholesale prices rising 18% in the first quarter of 1942. It implements the first round of price controls in late April 1942 along with wider consumer rationing starting in May 1942; this had already begun on the industrial level at the beginning of the year with the War Production Board limiting sale of critical military items like rubber. This helps a bit on the inflation front for the items it does control (there's politics involved in what it's allowed to do), but wages are up 18% and uncontrolled food prices are up a staggering 43% by the middle of the year. FDR gets another bill through (at the cost of the job of the original OPA administrator, who is blamed for all sorts of things by Congress) in July, and price controls are extended further. This still doesn't work completely, and when Jimmy Byrnes gains further power at an administrative level above the OPA, the response for a 10.9% rate of consumer inflation during the first quarter of 1943 is to finally impose a rollback, implement full price controls, and keep consumer price inflation below 2.5% for the duration of the war.

Restaurants are trickier, and since I've not written on them before I'll give you a more thorough answer.

So consumer rationing initially targets the items most critically short like sugar or that are needed for war production like tin. Fresh fruits and vegetables were never rationed, but canned ones were done so with great severity because of the metal required; this meant things like canned pineapple were an expensive luxury when the point system began. (This also meant that victory gardens were more symbolic than anything else; you could always buy pretty much everything grown in them without restriction.) But note that the vast majority of food is still not rationed at this point (hence the 43% rise in uncontrolled prices); for that matter, neither is gasoline. The latter is a political hot potato until FDR finally gets told outright that the United States - providing roughly 2/3rds of the world's supply at that point - is going to run out of capacity by the beginning of 1943. At that point, he very controversially adds it to the list in the middle of 1942 for the East Coast and then expands it westward throughout the rest of the year to where it's nationwide by December. For the rest of the war, it is probably the single most hated addition to the ration list.

So if you step back a bit, that first round or two of consumer rationing only affects a few dishes at restaurants; it's mostly about cooking oils, sugar, and canned fruits. The way restaurants operate in that era is to collect ration coupons from individuals for serving something that contains them; the whole initial point system and how it handled fractionality (you weren't turning over a full coupon for a single dessert, for instance) is a headache that I won't get into, but they did collect some, and for 1942 they'd take that collection and turn the customer coupons in when they went shopping themselves for more oil and sugar. But when January 1943 rolls along and significantly more items are added to the rationing list like meats and dairy, this becomes bulky and untenable; instead, restaurants are given their own set of ration coupons based on their previous business and customers don't have to turn theirs over. This somewhat resembled the wartime restaurant system in the United Kingdom as discussed by /u/Bigglesworth_.

This creates other headaches but also serves as an effective safety valve for consumers to spend some of their boomtime war pay; if you've got cash in your pocket, you might as well use it to enjoy yourself. Restaurant demand immediately goes up 25% in some places and by later that year in New York, it outright doubles. In response to the massive demand at restaurants, the OPA declares meatless Tuesdays and Fridays even at them, and really cracks down on price controls; toward the end of the ~90 days of each ration book period many restaurants would run out of some items.

But it's also important to note that even then the components of those items were still very much available in grocery stores, which served one of the main goals of rationing: to prevent shortages. Essentially, rationing cracked down on marginal demand and inflation that would have been unlimited otherwise. If you wanted to waste your gasoline ration driving around trying to find a piece of apple pie, you were welcome to do so, and for smaller grey and black market transactions you stood relatively little chance of getting caught and shamed (or prosecuted). But the most important part was that you could still get pretty much any item if you played by the rules and cut back a bit, even if it meant you had make a choice between a roast or a pound of butter for that week.

All this was enough to get through the war, but it created major headaches for Truman in 1946 when price controls were lifted and inflation boomed.