Here’s a quick build I just finished: A Raspberry Pi running RetroPi, installed in a Makita powerdrill briefcase with a 7″ TV and four USB controllers. Also included are all the components necessary to power the whole setup: A 12V PSU that powers the TV, and a 12V to 5V voltage regulator that powers the Raspberry Pi and the USB hub.
The USB ports on the Raspberry Pi would’ve actually been enough to plug in all four controllers, but I wanted to be able to plug in a keyboard as well without unplugging any of the controllers.
I didn’t bother properly documenting the build, since there is nothing fancy here: All the components are simply zip tied, pop riveted and velcroed in place. The only thing of any note is the power system: The wires from the PSU split into two sets. One set goes to a connector that plugs into the TV. The other set powers a 5V regulator that I got off eBay. The output from the regulator is again split in two, with one set of wires powering the USB hub. The other branch is connected to the micro-B end of a micro USB cable I cut in half, which allows me to power the Raspberry Pi without a proper USB power source.