I would also consider thinking about putting the autograph book in a ziplock bag-they fall apart if they get wet and ours mildewed. I was able to save the autographs by scanning them and fixing up water/mildew marks.
This is an excellent idea! We did the same thing... put the books in a ziploc, and then in the backpack... when we arrived at the meal we would take it out when we finished it went right back in the pack.