Here are some ideas:
* Watch Disney movies!!! All of the Pixar movies are great and watching the Disney Sing-A-Longs, especially
Disneyland Fun, are fun and helpful for introducing the giant characters at the parks and character meals.
* Also, coloring Disney coloring books and reading Disney story books is a great way to introduce the Disney characters and their stories.
* Making an autograph book w/character stickers.
* Watching the planning DVD is a great way to get a view of the parks and a little of what to expect regarding rides.
* All of you get in shape for a ton of walking, by walking - practice pushing the stroller w/GS in it.
* If GS doesn't like the stroller, get him used to walking AND holding a hand, or practice w/a safety leash if necessary.
* Discuss what to do if he gets lost, is in a loud show, how he should behave in a restaurant, etc. My kids have always done much better when they know what to expect and what we expect!