Take pictures of the damage done to your car due to the accident. Be sure to take photos of both the interior and exterior, from close-up and from far away, so that the insurance company can get a good idea of the extent of the destruction.
Write down how you are feeling physically after the accident, as not all personal injuries are obvious directly after the event. Try to take note of the same information for any passengers in your car.
Make note of any personal property inside the car that was damaged during the accident. This may include a CD player, laptop, purse, sunglasses, briefcase, infant car seat, cell phone, or any other item that you will have to repair or replace due to the accident.
Write down a description of the car accident from your point of view. You will need to do this for the police report, but you should write this information down anyway if the police do not show up. It can be given to your insurance company to determine damages and fault.
Do not admit guilt, as your only job at this time is to make notes about the situation, exchange contact information with the other driver, and cooperate with the police.