I've put my MMC64 into a cartridge case to better protect it.
There's a slot for the SD card (obviously), a reset button and two DIP switches.
Switch #1 is used to put the MMC64 into flash mode, so I don't have to open the case again and mess around with jumpers. (Switch #2 is not used.)
Here it is plugged into an SX64.
And, a 64C.
I will never use the clock port or cartridge passthrough, so they are hidden within the case. Yes, I had to remove the cart port connector (a very unpleasant process!
) But I think it's much nicer than having a bare circuit board, especially when carrying it around.