Car camping? All right, if you mean you are driving to the location, you simply put the things in the trunk and possibly the backseat depending on how many people are coming. If you are going to sleep in the car, then the trunk is still the best way to go.
Make sure that you put food items together and never seperate them otherwise you may find yourself with some overly friendly animals. You will need to fold your clothes as tightly as possible so you do not waste space. If you have a tent, place it in the trunk last... otherwise you may out too much weight on it and damage it.