Anything can turn into a book bag! I've used everything from plastic grocery bags to military-style duffel bags... Whatever it takes to haul my books home from the libraries, bookstores, and book sales that I've visited.
What are you currently using to haul your books home??? I'm using this Plano Fishouflage Crappie Bag that I found on sale at Farm & Fleet! Not only is it small and convenient, but I use one of the lure boxes as a pencil/pen case and the tags as bookmarks!