if your that worried about safety , you should wear a hard hat all the time
Easy to joke around when you haven't been in the situation. I can tell you from experience what happens when stuff flies forward in an accident. I have seen it too many times to not be weary of it. I have also heard stories of the aftermath (roommate is a LEO and his dad was fire chief before he retired. You couldn't imagine the stories I have heard from them about the scenes of accidents.) For instance, a 6x9 box in the back window tray (see it all the time) can be deadly if it hits you in the back of the head after you slam on the brakes because of a kid, dog, car, etc runs out or pulls out in front of you.
I don't need a hard hat. I just keep stuff out of the back tray that can fly forward. Then again, I don't keep very much in the car anyway. That isn't a safety thing though, I just don't clutter the car with junk.