J.K.
We took a road trip this spring with our 2 year old boy and 5 year old girl. The 5 year old was a lot easier to entertain, but our son did pretty well. Just have lots of snacks and little toys. Our kids really like to look at books so we got a lot of use out of the look at books we had taken along. We got the whole series of "My first books" They are by BK books and have subjects like Trucks (we actually lost that one along the way and it was his favorite), colors, Christmas, words, animals that kind of stuff. They just have pictures with the words describing them. The motion of the car kinda rocked him to sleep and he slept more than he usually does. We did a combination of train, planes and cars so we weren't able to pack too much, but if you are driving the whole way, you might be able to pack more of a variety of stuff.
Plan on it taking longer than it would if you were alone. Stops last a lot longer because they don't want to get back in the car right away. Good luck and have fun.