Well, to fill your time:
1. If you're flying, make sure you have your ground transportion nailed down.
2. Have the broad strokes of your daily agenda's on paper. You won't be able to do detailed plans until entertainment schedules come out, but it will help to know your touring plans. (BTW...share these with the kiddies, if you have some. I've found that my boys are willing to bypass attractions if they know when we'll be coming back for them.)
3. Start planning your scrapbook! Buy a book and paper. I know some gals start their layouts before they leave...I can't do that, but I do have the materials purchased and ready for the photos.
4. Buy 2 gallon ziplock bags so you'll be ready to pack when the time comes. If you're super-organized, label each one with the outfit that will go in it.
5. Start looking for fun tips. For example, if you can find glow-in-the-dark hair gel, buy it for the day you're doing the dark rides. I couldn't find any last year, but I'm going to start looking again soon!
6. Are you a penny squisher? Put together your M&M tubes of quarters and pennies so they're ready to go.
7. Prepack your fanny packs/backpacks, etc. Ditto anything that you won't use in the next two months...like maybe swimsuits.
Hm...that's about all I can come up with right now! Somehow I do all this stuff early and it still always feels like I'm rushed to get everything done on time!