How much damage can the average adult human body take?

Not much, Mate. One meteor or bullet and it's pretty much fertilizer time.

Edit by Tanmanknex: Well, it depends on where the damage is taking place and how severe it is. For example, if one person was shot in their hand and another was shot in the head, one would probably survive and the other would probably not. Saying this, almost anything in the back of the head, heart, and the back of the neck is more susceptible to severe injury from damage than other areas.