My husband bought a book at a thrift store and after he brought it home and started reading it, he noticed it didn't lay flat. Thumbing through the pages, he found a woman's checkbook with about thirty unused checks tucked in the back. He contacted her immediately and she told him she had moved recently and donated a lot of books, but she had no idea how her checkbook would have gotten in one! She was so relieved to have it returned to her and grateful that there are still good people in the world. (If you know my husband, you know he is good to the core and I love that about him!)
My lesson learned is that from now on, I think I'm going to double-check every item that is set to be donated to the thrift store before I donate it, just in case! You just never know what gets tucked into things.