I try to follow make sure I pack the following for all vacations, not just WDW...
2 pairs of old undies per day...change in middle of day...throw out old pair each time. This leads to the need for 2 liners per day so count before packing. I seem to be cooler if I change clothes during the mid-day rest. I also try to change shoes, too...but I don't throw out the morning shoes

ALthough I remember one time I had a pair of very very old sneakers I wouldn't get rid of. Finally took them on a trip and threw them out at the end.
Large band aids, I think they are 3x4 size. About the only thing that will stay on my heels.
My pink flask...a gift from my dear mom. Place in double ziploc baggies in luggage. A girl needs a nice adult beverage at the end of a hard day of touring. Put on robe, send DH to the ice machine, ahhhhhhhhhhh
Allergy and cold medicines (day and night kinds), eyedrops, other meds
Mints and Hershey bars, for when I need a sugar fix
Extra scrunchies/hair things because guaranteed, one breaks on the trip!
Extra shoelaces for sneakers (see above)
Melissa