A countdown chart or activity of some kind is always fun. We usually do a caterpillar. I copy Disney character clipart into Word and cut strips of paper, one character per strip. Then I write the number til our trip, counting down to 0. We link the strips together to make a chain (or caterpiller) and each day my kids take turns removing one link. They have fun seeing which character they get and how many more days til we leave. The fact that the caterpillar gets shorter and shorter really helps them anticipate the trip. You could do the same thing with construction paper strips and stickers.
It sounds simple enough, but having a really good packing list is essential so you aren't stresed about what to bring. I have a GREAT one, if you 'd like me to email it to you. At the least, make a list of the things you want to take to the park each day so you can refer to it before rushing out in the morning. You might include things like tickets, reservation numbers, photopass card, camera, sunglasses, autograph book (see below), bandaids, rain ponchos, tissues, hand sanitizer, sun hats, sweaters for evening, etc. It sounds like a lot, but it easily fits in one backpack that you can put on to go on rides.
It is always fun to do one type of "collection" at DW. Our kids do both autographs and pressed pennies. Many do pins. They are always a fun momento when you get home and can look them over.
Are you planning on doing a character meal? My kids (3 and 5) always look forward to these. Our favorite is Chef Mickeys.
You are going to have a FABULOUS time! Take lots of pictures!