The goal of these items is first to give players a viable means of re-heating food, or keeping it hot. In real life, these items more keep things hot than warm them but in this video game i would take some creative liberties and say they adapted further to the coldening environment and added a small heater.

Secondly, they should be nice in group pvm situations as they will reduce carried weight, and help apply buffs.

Essenbehälter(Engineering): https://www.iwm.org.uk/collections/item/object/30028462 Put fluids inside, gives them the 'hot' property as though they were freshly made. Consumes oil when turned on, could function like a lantern in that regard and no longer heat food if its out of oil.

Insulated Tiffin Carrier(Metalworking): 
A quiver for food. I would make a normal one(like in the picture) at a lower skill level, and then make an Insulated version at 75 - 100 which not only is a food quiver but also keeps food warm. I don't know if i would allow it to reheat cold food like the other one, but if you do the prep work of making fresh food for a dungeon crawl or event it would be a nice bonus to keep them hot. If it can reheat cold food, it should probably be engineering too. For prepared food only, not raw.

I would also make these take the slot of your satchel (+50 stone capacity) so you are making a sacrifice to do it.