When I was a kid (pre-seatbelt law days), my parents would pack a lot of stuff on the floor up to the level of the back seat, then cover everything with some blankets.
They did threaten to pack US in the trunk a few times, but never actually followed through.... <img src="/images/graemlins/grin.gif" alt="" />
You do what you can with what you've got. All the survival gear you could own rarely surpasses a good helping of common sense.
Sue