I made this case to help protect a classroom set of Micro:bits. They also can be handy with maker projects in which you want to mount the Micro:bit using tape or glue. Use small zip ties to secure the bottom. A thin shelf keeps the top in. Snip zip ties in order to free the Micro:bit when plugging into a breakout board.
Feb. 2018 update: I modified the original to make a "JST" version that takes out material to make accessing the JST charging port easier.