In other books I've found notes on scrap paper (names, addresses, odd sayings), newspaper clippings, little worship cards from church (only in the really old books) most likely used as bookmarks. Once I even found a book with the questionnaire in the back (they use to do those, back before the rise of the internet) filled in by a thirteen year old Linda, my Aunty Lou. Bought that at the second hand store when it probably should've been a hand-me-down.
A new book is exciting only for the story printed on it's paper. A second hand has that old, dusty, dry smell unique to books, the pages are a little loose and it no longer sits flat. There are tears, dog ears, bends, it'll even open up to its most popular pages. A book that is aged with use (or even without, was shelved but never read for decades) has it's own story written without the author's knowledge.