You can see a complete list of body parts inside the CS. Just open the properties window of an clothing or armor, and open one of the drop-down boxes under
Biped Object. You can assign either a body part model or an empty body part to any of those. (I'm not sure about weapon though, I've never tried what changing that does.)
I believe any body part can be assigned to any piece of clothing or armor. Rings, amulets, and belts ignore any body part settings, they won't change the wearer's appearance.
Skirts and robes are special in that they always disable (hide) certain body parts unless you specifically set them to replace those parts instead. Skirts hide the groin, the left upper leg, and right upper leg body parts. Robes hide the chest, the groin, both upper legs, both knees, and both upper arms, IIRC.