Okay, I'm a 23yr old non-mother so all I have is my personal opinion and retail experience, but unless he is very excited about going to Disney - I know, who wouldn't be? - But if that's all he'll talk about, THEN get him something Disney related for Christmas.
If not, then get him something he can use/enjoy there. As you and another said, get a digital camera or a video camera (if money allows). Or something he can do on the way there (someone already suggested this as well) like a video game or music that he can listen to in the car/flight.
If the Disney trip IS his Christmas present and you just want to give him something tangible, then I would totally go with a guide book, to help amp up his excitement.
I know I didn't say anything new but... let me use a story from my childhood ^_^ I kinda wanted a baby doll for my birthday, so I let my mother know. I did in fact get a babydoll, but every other birthday present I got was babydoll clothes, accessories etc. I never told them (just my sister knows to this day lol) but I didn't want any of the accessories or lots of girly clothing. I only sorta wanted a babydoll.
My point is, it's really easy to misread children and go completely overboard. If he collects frog toys & you give him a box full of them, it kinda kills the love of collecting. (this actually happened to my adult aunt! LOL Everyone kept getting her frogs & eventually, she had enough)
But, that's just my opinion ^_^;; Now it's me buying my parents too many things (parents are horrible at writting wish lists! )