I've found a good way to get tire damage on the sides:
Pour a bit of black acrylic paint into a cup or something. Let it dry until it's hard.
Take a Q-Tip with some nail polish remover on the end and rub it in the paint until the tip is black.
The stroke it side-to-side wherever on the car you want the damage.
For crash damage, it's hard to beat the trusty hammer and needle-nose pliers. A hot glue gun or Super Glue can be useful for putting back together "uncooperative" wrecked cars. :happy: