I did this 2 yrs. ago with dd,then 11 yrs.old. She was getting too old for the regular autograph books ,which she had done before.
I bought 2 mattes 1-5x7 and 1-8x10. We took one in with us for Mickey and Friends at the Disney Visa photo in Epcot and the larger one 8x10 to the Princess Breakfast @ Akerhaus in Epcot.
We carried them with us on just those days and I brought a "Clipboard" to hold them on so the characters had an easier time holding them. I also used "clickable Sharpies" in about 5 colors .
I got my idea off this Disboard site just about 2 years ago and it really worked out well for us...Good Luck !