I was just there today.. Okay mine a more geared to kids, but I will share. I have tinkerbell leave a little something for the kids in our room each morning. Today I got yo yos, paddleball, squirt gun, bubbles all with some Disney character on it. Just a little pixie dust to start off their day. (Also, gives them something to play with while we all take a shower and get ready).
Other things I have bought for our last trip from recommendations from the Dis... I forget what they are called... but the little face cloth size towel that dries quickly in the car section --- great for drying off seats for wet rides or if it rains it is good for the stroller.
Clips (in the kitchen section). These were great to hold things onto the top of the stroller visor (park map or daily schedule) This way if anyone wanted to view it I wasn't always pulling it out of my bag.
Plastic spoons, forks, knives - always good to have a set in the room in case you bring back food to your room.
Power strip - god with so many devices these days you can never go wrong with bringing one.
face cloths - they usually have the ones that are shaped like a minature hockey puck sometimes with Disney design. But great to have in your bag for a quick cleanup while at the parks especially on those hot days.
First Aid - They always seem to have somme type of first aid creme, aloe lotions, suntan lotion. etc... I was hesitant on getting sun tan lotion from Dollar Tree and it worked fine.
One of my favorite tips was a night light.
Lemonade or fruit punch powder singles for your water. (the ones they have are diet but my kids don't even notice the difference). Also, just check the packs since some have 4 in a pac and some have 10 in a pac.
Eye glass kit. Great for those light up toys from the parks that need batteries.
Nail clippers/scissors - great for those toy packages you purchase that you need to have a PHd to open.
Glow Sticks - I sometimes buy these at Michaels. They come in a tube that is great for packing that doesn't break. I usually just get the bracelets. I usually bring a bunch with me. My kids LOVE passing them out to other kids while leaving the parks. We gave out a bunch at Fantasmic last time -- Our kids had a ball playing with the other kids around us and it made the time go by.
My all time favorite tip would be gallon ziploc bags - Each day I put an outfit for the kids socks, underwear, shirt, short, hairbow etc. Each morning pass the kids their bag and atleast I know they match and that I am not searching for clothing items.
Can't wait to see any other tips.