I have tow more versions on how to die interacting with cars.

Confirmed. Same thing happend to me a few days ago. Up on a roof of a building in the port of Elektro, I carried a Blaze double rifle in my hands and came like 1 meter close to the ladder when the triangle shows up and I press F. So my Char just starts to shoulder the gun and walks over the edge :D

Next thing, I could not even loot my dead body after returning to the place... but that might be another problem.

Confirmed. Had it already three times. First two times on unconscious person and third time with healthy normal person. Each time canteen or waterbottle disapears from my inventory and doesnt show up in other persons inventory or on the ground. I guess its not supposed to be like this, because a canteen could get empty - but sure doesnt go fully into the person! Empty food tins should disapear, okay. But canteens shouldnt.