Disclaimer: If the thought of recycling/donating board game boxes or folding rulebooks in half makes you cringe, this post is not for you.
A few years ago, I started consolidating my small box board games into these awesome photo boxes (available from Michaels here) and haven’t looked back. They fit two stacks of standard cards side-by-side, and close tight with a latch for each box. It feels great to be able to whip out the games like a briefcase, and the boxes are still modular so that if you can still throw one or two in a bag for traveling.
If you sell your old games often, you may want to keep the old boxes in storage in case something needs to be rotated out. Also, you may not want to fold your rulebooks to fit inside the photo boxes—almost every rule book is online now, and if one of the rulebooks in your collection isn’t it would be a great opportunity to contribute to that game’s BGG with a rule summary.
The only thing I don’t like is the handle—it’s a little too thin for the weight of a full case.