Magic: the Gathering cube packs
Leah and I have really gotten into Magic: the Gathering. Our favourite ways to play are sealed deck and Jumpstart, both of which involve opening new packs and making decks out of what you open.
Since it would be wasteful (not to mention expensive) to buy new cards every time we play, we only buy a certain number of packs each set and re-use the cards we open to make our own packs for later games.
We originally tried coin envelopes and a product called Cubeamajigs, but neither was as nice or convenient as the side-loading papercraft boxes I made with my Cricut.
The above SVG image can be imported into Cricut Design Space to make boxes of your own. Or, if you want to make a box with different dimensions, a tool called Templatemaker can make similar patterns.