Update - Here's the 2015 update for this project - http://www.thingiverse.com/thing:688566
Back in December I found a great mod where someone shoved an SNES into a pelican case. I wanted to recreate this, but using a Raspberry Pi for a portable gaming rig.
It took about 7 months of frustration, joy, anger, blood, fried boards, and tears but it is finally complete.
This wouldn't have been possible without the awesome work people have put into the Retro Pie and Emulation Station projects.
Here's a great walkthrough from Lifehacker - http://lifehacker.com/how-to-turn-your-raspberry-pi-into-a-retro-game-console-498561192
You can attempt to recreate my project, but I'd recommend using it as a template and make it your own. I've included the blank pieces that should fit the interior of the pelican case so you can modify it to you heart's content. I've left off the accent pieces that I printed in white. They helped hide the seams of the separate prints it took to put the faceplates together.
The entire thing is waterproof and probably weighs 3 or 4 lbs. It probably wouldn't make you super popular with airport security, but the whole thing is portable. I've got a 16gb SD card for the main operating system and a 16gb flash drive for extra storage. It can boot into Raspbian and features wifi so you can ftp into it if wanted. Unfortunately there is no way to externally power the system while you are using it, but they are beefy lipo batteries that should hold out for several hours.
I was able to get about 7 hours while plugged into an external HDMI TV with the internal screen powered off. If you were to play it using the internal screen, it would most likely last for 3ish hours.
I'll post as many of the parts as I can find, but good luck and godspeed!