What kinds of things have you found in used books?

This question is meant literally. I’m an avid reader; I get lots of hand-me-down books to read and I’m a huge fan of the library. I absolutely love when I find random things inside used books, like notes or, in the case of the last library book I read, a hand-made paper flower. I don’t know what it is, I get such a thrill out of it. I find it kind of romantic that somebody and I enjoyed the same book and they left something in it, a small clue to who they are.

That paper flower was the coolest find yet. What kinds of things have you found in used books?

Edited to add a follow-up questions: When you find something, do you leave it in the book or keep it? Have you ever intentionally put something in a book for someone to find?