One thing (being an allergic person) I don't buy pre-packaged snack foods for myself because the prices are OUTRAGEOUS. $7 for a package of 5 tiny nutrigrain like bars for wheat allergic people, that's insanity.
Every once in a while I'll buy one of those items as a treat, but not as a daily food item.
Allergic people don't need packaged foods any more than non allergic people do.
One thing I do is settle on 8-10 dinner plans that are quick and easy to make from fresh ingredients without spending tons of money, and then I have 2-3 lunch or breakfast options that I keep on hand at all times. If one gets old I get rid of it and switch to something else.
Novelty and variety are budget killers. A person can eat oatmeal 5-6 days a week and switch it up on the weekend with something a little more frisky or time consuming. Needing a different cereal, or packaged yogurt etc that just gets really expensive.
We have available at all times:
Cereal (I buy ONE type of whole grain no sugar cereal for times when we're rushed)
Eggs with fruit or toast (we have chickens.)
Yogurt with fruit or toast
Sandwich pb and J or meat/cheese/lettuce/tomato on whole wheat bread
Leftovers from dinner and either option of course is flanked with fresh fruit or veggies
Dinner: (not necessarily in this order)
Roast chicken mashed potato night
Fajita night (homemade tortillas are so multi-purpose, like lunch the next day)
Mom's lazy night (pick through the fridge and throw something together)
Each of my dinners generally has a green salad and bread added to it. I am allergic to bread so I don't eat it.
Anyway that's how I do it. I limit what comes into our house. That helps a lot with waste, or things going bad. Snacks are fresh fruits and veggies, homemade bread, popcorn, cheese...leftovers.
Oh almost forgot, we don't really buy beverages. Milk for the milk drinkers (I don't let my kids drink it like water though) and we drink water. Special occasions I get cider. We 50% of the time have OJ, though we try not to drink our calories. Bad for teeth and your wallet.