Use bog (body filler) available at practically any auto store, or if they really are just light scratches or stone chips you might get away with some glazing or stop putty. Personally, I use a nitrocellulose (lacquer) based stop putty which is red in colour, because it's cheap and readily available - again at practically any auto store. Some people hate this stuff (which I did at first, too) and recommend an epoxy based stopping putty.