[MuGen]

Well if you want something where you can switch between games, and have games that are worth switching too, you should invest in a PSP but I highly doubt anyone will take this statement seriously)

PSP's intial library is full of great gaming, and if you buy a Pelican Extended Battery or even a Power Brick, you can have hours and hours of gaming with PSP's games.

Pelican Extended Battery - Runs on 3 AAA Batteries and it's own Li-ion supplement, which brings PSP's battery life to 10 hours and if a high end game is being used, up to 8 hours.

Power Brick can store 2 full charges, and before you go on a lengthy road trip, you can fill it up, and then when you're playing you can charge it up with the brick and no outlets are needed.

I'd definitely spring for the Extended Battery from Pelican though.

But since this is a DS thread, and you seem to be more interested in it, You should get some racing games. (RRDS and NFSU2DS) that should fill your needs on the road.