Brent,
I agree that having a reasonable stock of multivitamins is a smart prep item. Even if your calorie intake is low, a supplement would help avoid illness.
There are 2 primary things to keep: multivitamin, and Vit C. Unless you have a specific need, that's the short list. I take one particular other supplement that is the difference between being a cripple/needing surgery and functioning fairly well. That particular pill I stock up when I drop to a 10 year supply (30 bottles?). But I give them away regularly to people I meet who could benefit, so I never have 'old' pills. Not that expensive, $20/bottle.
One more thing for some to think about as a 2nd-level prep. The problem with Vit C is that your body only absorbs 5-7% in it's normal form, and if you take too many it'll flush you out. There is something called 'lecithin vitamin C' (google it). It's expensive, but you can make it with just water, alcohol, vitamin C powder, and lecithin. Tools are just a blender & little heat/refrigeration. The key advantage is that you can get 90+% absorption. And when you are fighting an illness, the one thing your body really wants/needs is Vit C. BTW, I got something like 10 lbs of Vit C powder. Way overkill, that will do 50 people with a daily doze for (years?), a long time. I don't have enough lecithin to mix it all, but I have the Vit C, so no big deal (and again it wasn't that much, $50 maybe, can't remember). And you could take the powder straight up rather than pill form. But the lecithin form is a nice all-purpose anti-illness preventative/treatment.