some fiberglass, sand paper and paint
Depends on the crack I think. I used bondo on some bad parts on my car.
if its a little ding use some fiberglass resin+hardener on the outside and for cracks you want to remove the bumper ect. place some fiberglass resin on the inside and cover the surrounding area of the crack. From there place a sheet of fiberglass over the crack and cover with FG resin+hardener. Then place a sheet of garbage like plastic over and re enforce it with something (usually clamps and wood). once all is dry sand down the excess resin so the body is smooth. You can then quickly spray some primer; once dry, paint! =)
I had to do this on my last celica with a kit after some girl cracked my rear bumper while I was sitting at a red light.
Power in Balance90 ST coupe- Sold95 ST hatch- Dead :(02 Impreza RS- DD