Mythbusters did a good segment on this!
I have not seen it yet but I looked up the episode from their site with the description.
If I can find it I will definitely watch it.
Killer Tissue Box (Aug. 3)
In a car crash, could the tissues kept on the rear shelf of your car be propelled forward with enough force to crush your skull?
My guess is that a Kleenex box wouldn't be heavy enough to do much.
Then again I might be wrong.
What does a box of Kleenex weigh and how hard does it hit at 30 mph and at 60 mph?
and in real life there is friction and air resistance.
Balloons will actually not move much in a crash as they are about as dense as the air is.
So what was their answer Mike?
You have me really curious now!