I have a laser pointer which takes two double A batteries for power, and I want to power the laser pointer with my car battery. How do I step the voltage down, and keep from overpowering the laser?

This could be done with a simple dropping resistor, since the car battery has lots of energy you can afford to waste.

However, consider just charging up several sets of AA batteries at home, or even from one of those chargers that plugs into a cigarette lighter. That would seem to be a much neater solution.