Another trick is to boil water, pour it into a Nalgene water bottle, and keep it in the bottom of your sleeping bag to warm your feet.
To keep warm while car camping, make sure you bring an insulated sleeping pad with a high R-Value, a sleeping bag with the appropriate temperature rating, and warm layers including a beanie, gloves, and thick socks. I’ve found that having a campfire and eating a small snack before bed also helps me stay warm while car camping. Another trick is to boil water, pour it into a Nalgene water bottle, and keep it in the bottom of your sleeping bag to warm your feet.