Elbows and Knees
These are the pointy bits that tend to poke into the pavement when you come off your bike. If you want to keep them, armor them. At the very least, make sure your outerwear has reinforced elbow and knee zones. For added safety, or if your leather jacket isn't at least 1.2 millimeters thick, consider mounting armor over or under it to increase the distance you can skid before the skidding cuts through to your skin.
For all the items on this list, the gold standard in testing for motorcycle protective gear comes not from the good old National Highway Safety Administration, but from Europe. Look for "CE-certified" elbow and knee (and everything else) protectors, which means that when the testing body smacked the front of the armor, the force measured at the back of the armor averaged less than 35 kilonewtons (the standard measure of force).