Yes, you're in a car, and not in a plane with tiny overhead compartments and minimal under-seat storage space. But that doesn't mean you should pack everything you could possibly need. Why take away precious leg and elbow room in your car when you'll be inside it for hours every day?
Minimize your load by packing clothing in basic colors (black, gray, white, red) that you can mix and match. Consider clothing made of lightweight, wicking fabric that can be washed quickly and dried in your hotel room if necessary. If you'll be on the road for a few weeks and will need access to a washer and dryer, make reservations at a hotel with laundry facilities or find a Laundromat when you get to town.
Check out packing lists and tips on trip-planning Web sites such as Planning-Fun-Road-Trips.com, which has lists for specific types of trips, including camping, couples-only and beach [source: Waechter].