Both of my kids like to read. Buying new books, or even downloading them onto the kindle all the time isn't financially practical. However, a trip the library weekly, or bi-weekly is! My kids like to max out the amount of books they are allowed to checkout at one time, so they each come home with 12 most visits. I needed a way for them to keep track of their books and their library cards.
The library had bags for sale (2 pounds)...I gave the kids sharpie markers and let them write their names on the bags and doodle if they wanted. I took a binder ring (available anywhere in the US or at Rymans in the UK) and attached a velcro pocket to the handle of the bags. In it, the kids keep their library cards and the list of the books that they currently have out. That way they can refer back to it when it's time to gather up the books at home and return them!