Although a coolers main function is to keep food cool or cold while traveling to a picnic or traveling anywhere a cooler will help insulate and keep food warm as well as long as you wrap the food in towels and foil to help keep the food from losing the heat.
You can also buy heated 12 volt lunch bags as well that you plug into the 12 volt system in your vehicle and it keeps the temperature up to keep the food from going cold while traveling.
I have one of those 12 volt lunch bags and it works great at keeping my food warm and I wish I had bought one sooner.