That's the age where the autograph madness is at its peak, I believe.
Autographs are actually an inexpensive (money-wise... not time-wise) souvenir. I purchased a book about seven years ago for $6. They probably run around $8-10, now. They sell a variety with photo slips that are more expensive but have less autograph pages (we purchased this kind at DL for the 50th anniversary and ran out of space by the end of the week).
It's also inexpensive to make your own autograph books. They can be as simple as index cards or pages cut in half, then folded in half and stapled in the middle (we created some like this for a group of kids to personalize) and as elaborate as scrapbook paper, photo slips, laminated covers, and spiral bound books. I believe some DISers have posted photos of their hand-made creations on the boards. Try searching Autograph books.
As for pens, you can buy an 8-pack of thick crayola washable markers. Sharpies also work well (but are permanent and more expensive).