I haven't had a long car drive to a con but I did take two day long trips to my family. Four days for when we moved from Missouri to Florida. Granted we stopped at hotels but still we were in the car for 10-12 hours at a time. My siblings and I often had books, our portable game boys (we had been given game boy colors coming from England to keep us occupied on the plane.) or even an mp3 player.
Another fun thing to do, especially with our sibling rivalry, the alphabet game. You look for signs that begin with the letters of the alphabet and you go all the way to z. It's not as easy as you think and it kept me and my siblings going for at least an hour due to us being stuck on certain letters. There is plenty to do to make long car rides less miserable, just remember to get out and stretch your legs every few hours, maybe 3-4 hours because by sitting still for so long you can risk clotting your legs. Don't try to take the 10 hours in one stride, but by doing these little things it'll make the trip go by a lot faster/smoother.