Yes I remember the BV (Boiling Vessel) in military vehicles from long days and nights on freezing north German training areas. They were indeed brilliant, you could you throw in a can of 'Baby's Heads' (steak and kidney) from the 10-man ration pack and it was piping hot in a couple of mins. And tea (always 'NATO Standard' ie milk + 2 sugars) any time you wanted.
Perhaps more practical for Cali'ing (if your gas runs out) is the US MRE individual ration, which has a self-heating pouch. Quite clever although not so convivial as the BV.