Z always has a book in her hand, usually with her nose stuck in the pages. When she's asked to do something else that requires she put her book down, she inevitably leaves the book where she is and grabs something nearby to stick into it to hold her place.
Things I found wedged into one or another of her books today:
1) My laptop.
2) Another book.
3) The schedule for her soccer games.
4) A dirty plate from lunch.
Note the lack of actual bookmarks being used here.