Here is my case design for the Adafruit M4 CAN Express & 128x64 Oled Featherwing combo.
I'm sure this may also fit with other feather boards as they are the same footprint.

There are some hardware required to complete this casing but they are just the following:

• 4x M2.5x3mm Heat inserts
• 4x M2.5x20mm Bolts

The assembly of the boards can be a little fiddly due to it's size but lowering the feather in first and then securing your CANBus wires in the screw terminals before adding the Oled Featherwing and lid then finally the 4 screws to hold everything together.

This was created of the need to carry around the boards while developing a project which is still ongoing but I found it a useful enough design for my purposes.

Enjoy!