What is the best way to build a battlebot with a remote control car?

For my physics class we are building battle bots from remote control cars. I was wondering what is the best way to do it. What kind of weapons could be operated through a remote and how could I mount it?

Some rules are:
cars max length width and height 24 inches all dimensions
no projectiles
no cords or control chains to operate the car

Unless you are "allowed" to build your own RC remote/receiver, hacking an existing RC remote will be a pain in the butt. Of course if you are allowed to build from the ground up, you have tons of options.