couponr- for a week at WDW, I buy each person a medium sized one. Part of that is the thought of rubbing something on my feet that has been already been all over someone elses feet.

One year we did small ones for everyone, and I ran out and had to use DD's. I put a good coat on my feet every morning before going out to the parks, and I put it on all over because I can get blisters anywhere the shoes touch, not just my heels. We don't take mid-day breaks, but on the rare occasion we were to come back to the room for some reason- then if I took my shoes off, I would probably re-apply before heading out to the parks again. DH is not blister prone, so he only puts a little bit on his heels just in case, and he could probably use a small one for several trips before running out. DD (6) obviously doesn't have adult sized feet, so she can get by with a small one for a week easily too. I'm really the only one that needs the medium...but it would be a crisis if we ran out for DD and I so I don't take chances!