Here's a microwave that's not only mini, it's actually designed to work in your car, so you can heat up pop-tarts or nuke some links while you drive to work
You power it through your 12V cigarette lighter socket (produces 175W of power) or directly from your car battery (produces 660W).

Maplin, a UK electronics retailer (think Radio Shack), is selling a microwave that runs on 12 Volt DC power (produces 175W of power)  directly from your car battery

It's meant to be plugged into your car's cigarette lighter, which means you'll be able to heat up your burritos, cold pizza, or even ramen noodles while you careen down the highway at 80-miles-per-hour.  I suppose a microwave in the car could be useful if you're someone who regularly takes long road trips and would rather heat up your own homemade lasagna than eat rest stop fare. Or if you're a huge picnic fanatic who has to have food served really, really hot, which can't be achieved with silly little thermoses. Or you want to make your own hot, organic popcorn for the movie theatre minutes before you go in.

Just in case your lighter socket is malfunctioning or you're in need of a little extra juice to nuke that frozen TV dinner, Maplin built in the ability to hook this baby up directly to your car battery