I keep track of my projects and assignments for school using clear folders. I stick color-coded 3x5 cards in the front of the folders to label them, so they’re all reusable.
It might look like overkill, but its actually pretty compact when its all put together. And it keeps me from carting around old papers I don’t need anymore, as well as from having to constantly reprint things I’ve lost.
You can see more of this hack in my Lifehacks set on Flickr.