I don't know about you but all of my shoeboxes are about twice the size of a British 24-hr ration, at least of the one I have. In any case, however, I like this approach. I've often thought about the problem from this standpoint but I really haven't done much of anything with it. I should describe my starting point first.
My time in the army was when C-rations were still being used. They are a little similiar to 24-hour ration packs but with less instant drink mixes and no biscuits/crackers. So having canned items seems perfectly natural and normal to me. Even so, I'd limit the canned stuff to certain select canned meats. I like some a lot better than others, naturally, but some are especially adaptable to this application. For instance, old-fashioned deviled ham comes in just the right size container that doesn't need a can opener but it has a strong taste (for my tastes). But most canned or tinned meats are a bit large to eat all at once. Small portions of meat are the only canned items I ever considered--except for fruit cocktail, which always disappeared from unattended C-rations right away.
My thinking was to create a one-day allowance of food, which is what a ration is, and with some exceptions, package it all together, one day's worth, for use in the near future, only I never really got past the experimental stage, mostly because of a real lack of plans for any future overnight trips. Anyhow, my experiments centered around attempting to duplicate that which was found in a 24-hour rat pack. A basic problem was packaging things in a size for a single day's consumption. The exceptions were coffee and sugar, which I have always packed in a sort of bulk fashion. I take along coffee, sugar and sometimes oatmeal along on trips, so that part is down pat. For outings when I was going on overnight trips more than I seem to be now, I also took along some kind of bread which I never included in these experimental food packs. I did have some problems.
One of the reasons I included bread (usually some kind of hard dinner roll picked up at a supermarket on the way) was because I couldn't find a good substitute for the "biscuits, brown" that are a part of a 24-hour ration pack, although there are some close substitutes. But they don't come neatly packaged anyway and crackers need to be packed carefully. Another thing I discovered was that even at home, some canned or tinned goods need to be carefully stored, especially the kind with the easy opening top, or they can come open and spoil.
It's cheating but there are heat and serve meals that require no refrigeration that are good for including in a day's ration. The ones I'm thinking of come in a plastic tray and will just fit inside the large mess tin of a British mess tin set, which is perfect for reheating the thing over a heat source with water. The mess tin is also the best way to carry it. Two meals will just barely fit inside the large mess tin. They're about as good as any frozen TV dinner but a little light on the filling and that's another reason for the bread.
I also have a supply of so-called pemmican bars that I consider to be the "emergency" ration (only consumed when so ordered!). The ones I have (Bear Valley) are "all right" but not so sweet that you'd call them candy bars. They're also relatively big. In theory, one is included on a trip.
That about covers it.
