Some little things to add to a car kit would be a few little things to make a picnic more enjoyable.
Camp plates and cups and utensils
Napkins or small towels or old cloth diapers
Hand sanitizer =>60% alcohol
Water bottle
A large folding knife (I like the Victorinox Picknicker for this)
Can opener if not on the knife
Blanket
A butane stove
A small wok or saucier with lid
