I pack a cooler with food and an activity bag for Connor.
Since this trip is longer than our usual ones, I'm taking along more food than I normally do. I'll pack dry cereal and fruit for breakfast. String cheese and more fruit for snacks, sandwiches for lunch, juice boxes, raisins, these small milk cartons, crackers, and a bottle of frozen water. This prevents stopping just for food, not to mention the high price of a restaurant or the unhealthiness of a fast food place.
The activity bag is even more important because it keeps Connor entertained during the times he is awake. I pack a few of his favorite books, a couple matchbox cars, color wonder markers and paper (no drawing on the car doors!), a couple figurines, and my favorite thing, a wooden tray with paths for a duck, a train and a car. The paths are cut-out lines in the tray that let the car move along it. It's part of a larger activity set but it detaches from it very easily and is great for playing in the car. You could make something similar with a metal baking sheet. Make roads on the sheet with masking tape. Attach magnets to the bottom of some toy cars and voila, you have your own play road.
There's one new thing that we're taking on our road trip, a portable DVD player. A friend let us borrow hers, so I packed that and some of Connor's DVDs to use in case of emergency. He's usually pretty good in the car so I don't know if we'll need it, but it's certainly nice to have.
We're probably on the road by now, so I will let you all know how our trip goes when I get internet access again.