+1 on the mirror. Avoided an SUV last year whose driver was texting or something while coming up behind me half in the bike lane. Can't see every single car that comes up behind me, but do see a good percentage of them. Every little bit helps.
Never been hit from behind though. Closest I've come is three separate incidents of people trying to buzz me. Two of them were motorcycles, the other a kid in a jacked up Toyota 4x4. How you go down I would imagine is a function of how and where you get hit - bumper, mirror, etc. Hard to predict.