I just built an emulator for my son-in-law that plays old NES, SNES, Sega Genesis, and a couple of other systems (more from the 90's) that fits all inside an old NES game cartridge.
Here is a picture of the one that I am building with some fresh hot glue. I used thin double-sided 3M foam tape under the USB hub board and Raspberry Pi Zero, but locked everything in place with hot glue.
Here is a picture of someone else's completed project.