The main things I always make sure we have are:
-backpack for the parks
-zip lock baggies of all sizes to protect our stuff on water rides
-disposable ponchos packed in a zip baggie - one for each day in the parks
-pin lanyards for the kids
-water for the room
-body glide
-sunscreen
-medical supplies (band-aids, tylenol, etc.)
-small lanyard/purse to hold park tickets and fast passes
-small misting fans w/extra batteries
-phone charger
-camera/charger/extra memory card
-liquid soap for the sink in the room
-I make an index card for each day listing our ADR times and reservation numbers, park hours, parade times, etc.