This is a difficult subject to write on. Small children grow so fast and change diets so often, it’s virtually impossible to stockpile anything for any length of time. Often people without kids will suggest cloth diapers, but I’ve used them, and I can guarantee I won’t use them again unless there is no other alternative. They stink, are extremely messy and require huge amounts of cleaning and disinfecting. You can buy large supplies of diapers for reasonable cost at most big box stores (CostCo) and if you track your child’s growth you can estimate how many of what sizes you will need for a couple of years out. And if you get too many of one size or another they do keep forever, so you can use them as barter or just give them to another parent that could use them.
Another issue is food. Mothers milk is really the only way to go for the first year, to year and a half. You can buy formula in powder form but you will have to work out logistics for hot water to mix it with, and trust me, when your baby is screaming her head off for food now, you really can’t wait for water to boil over a camp stove in an emergency scenario.
Later on they will shift to “solid” food, which means jar food. If you read the jars you will find that the most common fillers are banana and apple. So, if you want to save a few bucks now, a good blender will get you a long way to feeding the young’un and in case of emergency the babies will be used to eating “real” food if jar food can’t be obtained. BTW most of the all fruit jar foods are pretty tasty for adults as well. Just saying.