This subject comes up periodically and so here is the newest version of this list:
Moderator Judy's & Larrison's Car Camping Gear list
Packing the Trunk (by RoadTrip Advisors: Judy, Larrison, Laura, Brad, Michael, & Mark) Plus, more commentary and suggestions from RoadTripper601, Uclid and many others. A great primer for packing your trunk.
The "perfect" tent for roadtripping
Personal Cabana Towel (PCT) An essential tool, if there EVER was one!
Travel Sized Products -- Is this a good idea? (posted by bluehighways)
Others to follow...