Lots of good suggestions here, and no arguments that any of them can't be perfectly appropriate. It's largely a matter of finding what matches the lifestyle of the one using them.

The "problem" with recipes by weight vs by volume is largely academic in the US now, since cooking scales are easily available ($3 to $7 US, at last look) with dual scales, ounces and grams. (Since every dietitian we've consulted has different preferences, we have several.)

I go a step past the "bulk stock" items listed above by skipping Walmart and going direct to Sams, where I buy rice in 18 to 28 lb bags, and dried beans usually in about 15 lb packages. Sugar and flour, for those who use enough, are available in packages up to 30 lb, but careful shoppers may frequently find that a couple of 5 lb bags of either, also usually available, is priced at less per pound than the big ones. (Sugar lasts forever, but flour can "go stale" without careful storage.)

My "staple food" is coffee, and the cans (even if plastic) make reasonably "vermin proof" storage containers for other dry staples once you finish the coffee. You do need to mark them clearly so you can tell which one has the lima beans and which is the navvies.

Canned beans, peas, and corn come in six-packs (or 8 can flats) and store well enough. Sams has less selection of frozen vegetables than retail stores; but mixed veggies in 32 oz (2 lb) bags are usually available, and there's no need to break them down if you have a good freezer since you just pour what you want in the pot and fold the top over the rest to go back to the freezer. The fresh fruits/veggies selection is a little less broad than at the retail stores, but we usually find what we like.

Surprisingly, perhaps, buying in bulk is more appropriate for one or two people than for a larger family, IMO, once you learn to break down the bulk and store appropriately.

Nearly all US refrigerators have a separate freezer section, usually about 1/4 or 1/5 the size of the 'fridge, so almost everyone here has some freezer space unless they need to stuff it with enough ice for a cocktail party for 30 on a weekly basis(?). I don't know if the fridge/freezer combination is the normal configuration elsewhere.

When helping an elder with menu planning, I'd suggest the possibility that "special preferences" are not unlikely, and may not be apparent to younger "helpers." Even those lucky oldsters who have some teeth left or have relatively good dentures may be less comfortable than you'd expect with foods that require more than a little chewing, or that have "gritty bits" in them. It may be hard to find out how many good teeth many elders don't have since some don't like discussing the subject.

Some may also have "deviant digestive processes" that you don't know about. With some, discussion is the appropriate approach; but some may be reluctant to discuss, so "sneaky observation" may be needed in order to be helpful. Sometimes, deliberately discussing the meal, with minimal reference to the subject's liking for it, is more effective; if you can listen closely. But one must be careful. Sometimes an "offhand comment" has real significance, and sometimes it's just an offhand comment - so be careful about leaping to conclusions.

For most "parents" of people here, some understanding of the general health of the person you're trying to help is probably essential, since maturity and wisdom often go right along with physical peculiarities not well understood by "the kids." (My kids are both charging hard on 50, and still don't understand me.)

John