How can I keep food hot for extended periods without an active heat source?
The long drive is easy. There are 12 volt cooler/warmers available that would cover that need. But you have to do your homework. I found several that say they heat to 140° F or above, but I did see a couple that don't go over 135° F. There are also reusable hot and cold packs that can be used in an insulated cooler or carrier that will keep food safe for 4 - 6 hours.

There are several other options that could be used for a long drive or camping, etc.


Instant, disposable ice packs or heat packs; don't require a heat or cold source and can be replaced as needed.







Hotpots - Transfer hot food to the hotpot and it keeps hot for several hours.





Hot pot casseroles - Food can be cooked in and carried or stored, staying hot for several hours.




Other ideas for camping:


A chafing dish type setup.
A camping stove.


*Both have certain time limits and shouldn't be left unattended.


If you use the 12 volt cooler/warmer you can plug it in as needed. However you need to be sure that you don't run your car battery down. You can avoid this by running the vehicle while heating/cooling. (Not the most efficient.) Also, in some cars (like mine) the plugs will not work unless the car is on.