I love road trips! I don't drive, but I'm a great passenger, and you can count on me to have what you want/need in my milk crate, tote bag or cooler.
I always make a bag up with prescription meds, tums, pepto bismol, and aspirin. In the milk crate go wet washcoths in a ziplock bag, paper towels, kleenex, snack crackers, squirt cheese, cookies and fruit.
I fill the cooler with bottled water, sodas, beer, a jug of milk, another of iced tea, and sandwiches in small ziplocks, then packed together in a big ziplock.
We allow ourselves one restaurant meal per day, and part of the fun is finding cool places to eat...like "Vince's" in central Illinois, an inconspicous little place that had wonderful gourmet food, including Shrimp Wellington that melted in your mouth...a little truckstop in Knoxville, Tennessee where a plump, rosy cheeked cook made biscuits that floated off your plate..."King Frog" in southern Georgia, where we were served plates piled high with tender, crispy frogs legs...and one of the best, an open-air bar on the beach of Anna Maria Island that served pitchers of beer with plastic bags of ice in them to keep the beer cold, and had fabulous fried grouper sandwiches, fresh shucked oysters and the like.
When it comes to clothing, I do always take too much, but I don't consider doing laundry part of my vacation. One must also take into account the possibility of weather changes. On two of our trips to Florida, we encountered unseasonable cold snaps, and I was really glad I'd included jackets and long pants. I use basically the same method as Claire. I roll up the t-shirts, and put socks or belts inside the shoes. I also make up an "overnight bag" with a change of clothes and necessities for everyone, so we don't have to drag in all the luggage for an overnight stay.