We actually had issues with the crayons on the plane. I even had the triangular ones so they wouldn't roll on the floor, but she still managed to keep knocking them down, and then DH and I had to dig around for them. (I apologize to the crew of AirTran if we missed any, we really did try). I like those "Magic" books with the one marker that makes pictures appear, or makes the colors on the pictures appear. Lots of fun, and only one marker to keep up with. I also found sticker puzzle books at Michaels. They come with several different designs, and numbered squares that make a picture when you put them in the right order. DD still needs some help with them, but they're good for working on her numbers. Sticker books were also handy. I've seen Mickey Mouse and Princess themed HUGE books at Sam's. That kept her occupied for a while on the plane. The best thing though, was the DVD player on the plane. Can't beat cartoons for distraction.
Disposable sippy cups were handy in the parks, as were baby wipes and sanitizing wipes and spray. As a PP stated, our ponchos were about useless. Next time we'll just take umbrellas and raincoats.
My best tip though, is channel 96 in the hotel room if you're staying on property. I've heard it's not at all the hotels, but it was at CBR when we were there. It's all classic Disney cartoons all the time. It was on almost all the time we were in the room. Great for winding down at night, getting up in the morning, and relaxing for a while when we just needed a break from stimulation. We even blew off Fantasmic on the night we were supposed to see that because DD was just too tired. We headed back to the room, turned on the cartoons, ordered a pizza (with Mickey on the box!) and snuggled into bed. I think we had a much better night than we would have had with a overtired, cranky, terrified toddler, and we woke up rested and ready to have another fun day!