What this is
This is a microSD card holder with a lid. It holds 10 cards (but can easily be printed for fewer or more).
Why I needed it
I bought a micro SD card and it came with a case, which I used for my microSD cards, but it didn't close very well. That led to the cards spilling all over my backpack, and I wanted something that wouldn't do that.
How I made it
I designed it in OnShape and went through a few iterations before settling on a design that would be compact, convenient and wouldn't open on its own.
I had some problems designing the lid, but in the end I settled on a drawer design. It's a bit small so it grips the holder (so it doesn't open by itself), but I added a bump and hole to provide additional grip.