In the past few years, we have covered a bunch of awesome Raspberry Pi powered gaming machines here. The AdventurePi is also worth a look. It is a DIY portable retro gaming rig that uses RetroPie to emulate classic video game consoles. It is powered by a Pi 3 B+ and has a SunFounder 13.3″ IPS display and 30,000mAh portable power bank.
The AdventurePi has a rugged, waterproof hard case that houses the electronics. The total cost is about $250 according to the maker. You can find the instructions and parts here.