Cooking with tins?

What's a hay box?

Its like a slowcooker that doesn't use any power or a homemade thermos.

Boil up your stew, beans, rice pudding, whatever in a heavy lidded casserole dish.
Find a solid box, pack the bottom with  hay, straw, shredded paper whathaveyou,
Put the hot pan in the box and pack around with more insulating material.
Put the lid on the box and walk away for a few hours. 

The pan carries on cooking using its own heat.
Plenty of Youtube stuff on how to make one.