take a deep cycle 12V battery and a DC to AC converter. Take the car plug apart, wire it to the battery. Then hook up a small TV, and a GC/Wii. Once you've got it all hooked up, start up the TV, then the GC/Wii.
You can probably play for a good 4-5 hours.
*note, I did this when we lost power in the middle of the winter around 8 years ago and the house probably dropped to ~40 but I had my blanked and was hiding in the basement which was the warmest place left 
EDIT: I wanted to note, I listed GC/Wii because they both take under 17W, and if you turn off WiFi you'll use even less power. I only had a 175W converter, so there is no way it could power a X360/PS3.
ok, so you don't have the equipment listed above? get out a good board/card game, and have a good family night. My favorite games are Ticket to Ride, Power Grid, and Bang!. Personally I'm looking into buying either Killer Bunnies, or Moto Grand Prix next.
