I too am glad to see this thread back at the top of the list! I got some great ideas here in the past.
* If you have or buy Mickey ponchos, fold them inside out when you take them off wet. This way the wet stays together and the inside stays dry for another use that day. It also makes it easier to put in a backpack and keep the bag dry this way.
* Bring extra hangers from home. I needed to hang Mickey ponchos to dry overnight in the room, and there never seemed to be enough hangers. I did hang them from the top corner of some doors and a mirror though
* I could not find kid-sized Mickey ponchos, so I had to use the $ store ponchos. Problem was they were all out of kid-sized there too, so they were way too long. I took along a small pair of scissors and trimmed the poncho down in the room before we left. Then it was ready to use later, and I threw them away since they cost $1.
* Buy poster markers at Walgreens for character autographs. These markers are like an inch around, and great for characters with big hands - makes it easier for them to handle. We've gotten so many remarks from characters and their handlers on them. I think they come 3 to a pkg and each end of the marker is a different color.
* Take a large (bigger than a gallon) Ziploc bag to put inside whatever bag you are carrying in the park. This way you can store cameras, video cameras, or fragile/paper souvenirs in them during rain or water rides.
* Take a Neat Sheet with you. This can be unfolded to sit on during parades and holds quite a few people - doesn't matter if the ground is wet or dry. It also makes an impromptu blanket if someone is cold. You can wrap it around shoulders or legs. Never used it for this, but I guess you could also lay it out on the hotel bed for your kids to eat on. That way crumbs or spills don't mess up the bed, and you can shake it out on the balcony or nearest outside exit.
* I saw this one, but second the idea of a shammy. I bought a lilac one at Target that came in a plastic tube. Great for quickly drying off wet chairs/tables/strollers. Then you can use it to wash the car back home.
* I take a couple of kitchen garbage bags. I put our dirty clothes in one in the corner of the room. At the end of the week I just pack it in the suitcase and I'm done. Then the clean clothes left don't get on the dirty ones and I don't have to fold the dirty ones back into Ziplocs or anything. If I don't have a Neat Sheet I've also used them to sit on for parades.
* I saw this one years ago and stole it. Buy an obnoxious scarf to tie on your stroller or backback. I bought a construction orange one at the $ store and it goes on every trip. We rented Disney strollers and this sure helped being tied to the handle since they all look alike when you park them. You can use the same trick for your luggage if you have the generic black, forest green and red that many people do.
* Glo necklaces have been mentioned, but I wanted to say that I buy these to help keep track of my DDs at night. Of course they aren't the only kids wearing this stuff, but it does help and makes me feel better in the nighttime crowds. I make them wear the same color necklace on the same night so I know to look for two "green" girls or "orange" girls.
