One item you will definitely want in a basic roadside emergency kit is a flashlight. Without one, you won't be able to get much done in the dark. You will also want a good set of jumper cables. This is an invaluable item when you need to get a dead battery going again.
Tire problems are one of the main roadside problems. Makes sure that you have a spare tire and the tools to change a tire. You may also want to have a can of fix-a-flat in your car. A small air-compressor that plugs into your car's power port is another great item in roadside emergencies.