http://www.themayfly.com/weblog/2007...zer_howto.html
^^thats a tutorial on how to make a car organizer.
you should always keep a pillow and a blanket in your trunk, especially now that its getting a little chillier.
keep a couple water bottles back there too.
you could get a little clip on light for reading so you dont have to turn on the light in the car.
maybe put some glow in the dark stars on the ceiling for when you go to sleep at night :]
you could keep some snacks in there.
keep some makeup remover wipes incase you need some refreshing up to do. it doesnt replace washing your face, but its the next best thing.
keep some travel size toothpaste and mouthwash. you can rinse with the water bottles in the back.
travel size deodorant and body spray?
a little hairbrush and some hairbands will come in handy for when you wake up
hope it helps, and good luck!