But everyone has some kind of flour, water, and salt. So everyone can have hardtack. Yum. It's hard, dense, and probably flavorless. The elites might eat better than the average soldier, but I think that depends a lot on who's running the army and what their support apparatus is like. Begnion's senators can probably expect to be served steak and crisp salad if that's what they want; the Dawn Brigade, not so much - at any point in the story. Daein isn't prosperous enough in FE10 to support good eating for its army. Unless they were skimming off the local harvests and stores on their way down to fight Sanaki's army, they were probably eating hardtack, dried meat, and lots of other dried stuff. I'm assuming they didn't have canned goods. That's a bit more advanced than the visible technology level in most of the games.
Anyway, this is what got me thinking:
With insect infestation common in improperly stored provisions, soldiers would break up the hardtack and drop it into their morning coffee. This would not only soften the hardtack but the insects, mostly weevil larvae, would float to the top and the soldiers could skim off the insects and resume consumption. Another way of removing weevils was to heat it at a fire, which would drive them out. Those troops too impatient to wait would simply eat it in the dark so they wouldn't have to see what they were consuming.
Having been scarred at a young age by an insect infestation in my kitchen, this makes me not want to eat for the next day or two.
Food storage before the late eighteenth century consisted of paper wrapping (and possibly an oiled variant?), cloth wrapping, clay pots, wooden boxes, and cloth bags. None of these are airtight. You could salt meat and fish, or ferment or pickle food, or preserve it in honey or fat, but it sounds like grain products were free game for pests, and I imagine this would've been especially true on the road. I'm not sure what the wiki is referring to by "improper storage," but I'm thinking wooden crates, cloth sacks, and paper wrappings are most likely to appear on a supply train for your FE army, unless you want to argue for some kind of magical preservation. (And why not? If you can heal wounds with staves and set things on fire with a book, you should be able to keep your bread maggot-free with a tome, too.)
Characters with commoner background were probably used to the preservation techniques and the problems with them - spoiling, infestation. An aristocrat, on the other hand, might have to be handled more delicately.
Nobody ever mentions this in fantasy, to my knowledge. When the runaway princess throws tantrums, it's because her skirt gets dirty, or she has to bathe in a pond, or sleep on the ground; I can't recall an instance where the princess opens her food packet, breaks off a piece of that awful hard biscuit stuff, and finds a weevil making its way out of her food and across her hand. I mean, who wants to picture that.
Usually, I bet high-ranking commanders get their food prepared for them, and this would be especially true of nobles. But that won't always be possible. A rag-tag group like Eliwood's isn't going to have cooks lined up to serve palatable food to Priscilla. When the allies break up in chapter four of RD, they don't have the manpower or resources for decent food preparation. They're going to carry what they can and scavenge the rest on the way. Meanwhile, they're going to have shitty storage solutions for their bread.
So you know, Rebecca's supports with Raven amuse me, and also strike me as a great opportunity for bonding, because she's cooking real food. Come on. After weeks of wormy bread and dried meat, I would love her!
Does Rebecca/Raven even exist? It has to. FE7 has been around too long for it to remain unexplored. :/
So anyway, this is a quick rundown on storage. I admit to not doing much more research than that. The food timeline has some interesting stuff - the official diet of the Royal Navy at the time of the Revolutionary War, for example. Not much else seems relevant. If you scroll down to the language arts section, though, I personally think "A Thousand and One Fritters: The Food of the Arabian Nights" could be interesting - or intensely boring, you never know.