Here is a link to the "case it" expandable file.

http://www.amazon.com/Case--Locker-...ords=Case+It+ACC-21+5-TAB+Expanding+File

Note that this is a component of a larger system that I have not used (but looks like a backpack alternative). We just used these expandable files and put them in DD's back pack.

The video on the link shows the whole system.