I think it would be cool if Items on your shoulders and a backpack would become invisible if you're sitting in a car. So you'd avoid all the clipping of weapons and backpack through the car. Now that we have crossbows they stick out even on the side of the car. I've actually seen some games do this and it looks pretty good.

For example the moment the animation of "sitting inside of the car" starts, the backpack and the weapons on your back slowly fade out. And the same way for when you're getting out of the car. Slow fade in.

I think that's a good compromise since another option would be to take off the bag and weapons and put them in the car before getting in, but that would be way too tedious and take away from the flow of the game. And given the nature of how fast everything can get "south" in DayZ it would be terrible if you'd have to browse for your weapon in car inventory seconds after you've been shot at, because 95% of people will shoot at the car the moment they see it.

cheers !