CD file closed
When you're ready to go, the file closes back up and everything stays in place by hooking an elastic band around the bottom.
Typical 3x5 cards are too wide to fit all the way in, but if you put them in vertically, they just stick out a bit at the top.
The closed file measures about 6" by 6" and the depth varies depending on how many cards you have; in this case it's about an inch and change.
Related 43 Folders post - "Using a kids’ CD filer for organizing index cards"