I'm using mine to keep all my grungeboard and chipboard inside. If you've not used grungeboard before, you might want to see Tim Holtz demonstrating how to use it here: http://www.timholtz.com/vid_grungeboard.html Its very clever stuff but smells oddly like leather! Karen at Scrapz was kind enough to give Rosie and I some to use and I liked it so much I went on her website and bought some more!
Of course you can use chipboard for the challenge if you prefer.