Treasure chest that can hold up to 20 SD Micro cards. Printed at 100%, this file should provide enough tolerance so that the cards will not get stuck in the slots. The lid keeps them secure, but there is enough room for thin foam if you don't want them to rattle.
The bottom will not require supports if printed upright. The lid will require supports, and can be printed upright for a clean outer finish. I printed my lid with ironing enabled in Cura, and got excellent results; not recommended for bottom.
Bottom and lid can be equipped with 3mm x 3mm cylindrical neodymium magnets, which are relatively inexpensive and super strong. The holes have built-in tolerance, but may require drilling for a clean hole. If your magnets are lose, some glue or epoxy should hold the magnets in place well (sand magnet before application). A piece of tape can be used between two magnets to make sure orientation and depth are perfect. I was able to press fit the magnets into the lid, but I had to drill out the holes in the case.