I re-use small travel size med continers for Advil and Aleve and use my label maker to mark them for their contents.
I also re-used the glass vials (which are available on the 'net new..I just forgot where) I got my new contacts in. My eye doctor also gave me a couple he had sitting around. They are about 1" high and about 3/4 inch in diameter. For small pills I can store 15 to 30 doses in these.
Pill size is a clear issue. But generally I try to get the smallest container I can put the most pills in.
I never travel with less than 30 days of personal meds. And generally have at least a weeks worth all the time.
My FAKs have a stash too.
Pain meds etc ...well ...the volume seems subjective to me and I rarely use them ...but I know in any emergency scenario that will change. But for now, all my FAKs have travel size containers stuffed full ... they normally only come with 10 pills and are only about half full.