I been using my 12 volt roadpro lunch bucket for the past 8 years. I do use it to cook frozen food now that I have a fridge. It takes about 30 minutes to heat up some fish sticks or taquitos. For can food like stew,soup,chili etc, it takes about 15 minutes to heat it up. It won't cook food but it will heat everything up. It uses about 4 to 6 amps to heat up most foods.
I just use aluminum foil to line it instead of the special aluminum inserts they sell. On mine I replace the cheap cigarette plug with an xt60 connecter and cut the wire as short as possible, it uses thin 16 gauge wire which gets very warm while in use. You can use it with the small lithium power generators, the 11 volts of those units is no problem, I use mine with my 65ah li-ion pack.
When you need a hot meal and don't got a giant battery bank, and don't want to mess with gas, this will work and gets your food very hot. It doesnt have an on off switch, I always use a audio timer so I don't leave it on.
I use it several times every week, and after 8 years, still working. Never had reason to use anything else.
Jonyjoe, great option for certain type foods. I have one similar coming...thanks