As soon as you've gathered as many of these items as you want, go ahead and put them in your bag, or case of choice; I used my Victorias Secret bag for my plane ride, but now I use my laptop case.
After step one, you can keep yourself with games, music, magazines, books, etc.
If you stop frequently, take your time to stretch your legs, or go to the bathroom. Holding, or waiting to use the bathroom isn't good for your health.
After you finish your trip, feel free to stretch, use the bathroom, etc., and also unpack your things from your car.