over the years, our favorite thing to get autographed was a photo book we created for each child. We took pictures from previous Disney trips and created a "photo book" (like by Shutterfly) for each of our sons. Each book may have pic's of other family members, but was primarily pics of THAT son at Disney through the years. We grouped the character pic's by theme (so Mickey together, or Little Mermaid characters all on 1 or 2 pages) and each son would spend time in line finding the right page for the character to sign, and it was also a great convo starter. We also did a few pages w/o any specific character, that way if we saw someone "new" there was still somewhere for them to sign. We made the 8x8 books so they fit in a gallon size zip lock bag with a few sharpies, so was super easy to keep up with. Years later, they still have those books and have dozens of signatures. - I'm include the "draft" screen from my shutterfly project to show you what the front & Back cover look like, and then 2 pages that I grouped together to highlight Stitch, which was one of both of my boy's favorites.
in fact, our oldest is now a cast member, so for his birthday, we are making him a "new" book with more current pictures so he can start working on a new signature collection.