Something else fun is to have them "autograph" books. I'm sure being a Disney fan you have some Disney Golden books or any one of a million other books with disney characters on them. Have them sign their book, this makes a very neat souvinier.
We did this at our character meals. We had a pooh pop up book that we took to Crystal Palace and had all the characters sign with a black marker as they came by. Piglet refused to sign the cover because he was not on the it, we found him in the book and he signed that page. It was really cute.
It's fun to say I have "Mickeys Big Day" (or whatever that book is) SIGNED BY THE BIG MOUSE HIMSELF