I vote for washing the car and cleaning it out in very hot weather. Plan on getting wet and this is always fun with the kids especially if the hose is creating a shower or a squirt of ice cold water. Do the inside first. Clean out all the stuff that has accumulated after summer adventures and then save the best for last and wash away the dirt and grim on the outside.
I do tend to leave some sand in my car for a pleasant reminder of a great memory.