Shelter......... when you're car camping. Check
Navigation, you should always have a road atlas in your car, one, because they are fun to browse through and dream of the next trip, and two, because they are helpful for navigation. A compass is helpful, but not necessary if you're in a car. Find any major terrain feature or intersection and you can figure out where you are from the map.
Water, good tip, always carry way more than you need. I inevitably fill up both my 7 gallon tanks even for weekend trips because the dogs get really sandy and a clean family is a happy family.
Knife, always good.
But real car camping:
Warmth (Puffy coat, wool blanket)