We used to cook up a stew or a joint in a casserole dish with a lid (like a dutch oven), and put it in a haybox for the day so we had a hot hearty meal at the end of a day outdoors.

https://en.m.wikipedia.org/wiki/Dutch_oven https://en.wikipedia.org/wiki/Haybox

But I've just found this and it looks excellent! https://en.m.wikipedia.org/wiki/Thermal_cooking