A little fun at my archives job — I got to copy family tree information that was written in an old Bible. The Bible, published in 1791, belongs to one of our docents and has been in her family for generations. They have taken good care of it! The earliest births and deaths were written on the blank pages in the front and the later, 19th-century information was written on ornate family tree pages in the middle.
Wonderful heirlooms like this always have surprises between the pages. Someone wrote a story and stuck it in this Bible. I also found a strip of cloth and a small evergreen branch.
What treasures have you found in old books?