It's probably a good idea to have some food stored in case some sort of emergency isolates you from the food distribution network temporarily, perhaps for up to two weeks. [1] Anything that did this would probably stop electricity, gas, and water as well. So this means water storage is actually more urgent: you need a gallon of water per person per day, or 14 gallons for two weeks. This takes up a surprising amount of space: if you buy gallon jugs of bottled water then for a family of 5 you're stacking them 3x4x5.

For food, my understanding is that the first priority is calories, then protein, then vitamins. I looked through a lot of options [2] to try to find the cheapest kind of food to keep that didn't require refrigeration, freezing, or cooking. I expected that the answer would be non-perishable food you store somewhere in case you need it, perhaps canned protein of some sort combined with hardtack [3]. Or maybe one of those emergency food supply buckets [4]. Instead, it looks like you do best to buy extra semi-perishable food you already eat. If instead of keeping one spare jar of peanut butter you keep three per person and always eat the oldest first, right there you have the calories and protein needed for two weeks. [5] Peanut butter keeps for a year, so you should be eating it before it goes bad. Do this with your multivitamins too, and you should be all set.

Really, I should have expected this: food that is optimized for longevity is going to be more expensive than at least some food you already will have around.

[1] If the problem is not temporary, then you're probably screwed: at least where I live there are far more people than the land could support, not even considering the time it would take to ramp up agriculture. Even if you had plenty of food saved, I can't see you keeping it. If you live in a rural area you might be ok, but the local farms are probably either very small or massively dependent on non-local industry.

[2] You can see my notes in this spreadsheet. I was quite surprised that peanut butter was cheapest both per gram of protein and per calorie.

[3] Known today as "pilot bread" and apparently really popular in alaska.

[4] Not only do these need to be combined with boiling water to eat, so they're not a good fit for a situation where you may be without a stove, but you can't just say "275 servings means 275/3 days". From their nutrition facts their servings average 130 calories, so to get 2000 calories a day you'd need fifteen servings. At three meals a day it's really a 55-meal bucket.

[5] You wouldn't enjoy just eating peanut butter, and it might make you sick, so you should do this for a variety of foods. Peanut butter is just the cheapest I've found per calorie and per gram of protein. (Some comparisons). If you were really just eating peanut butter you'd need some sort of grain product to complete the protein, so you should consider that too.