I found that in practice the spirit burner was not very efficient in cold conditions and the fuel was not always easy to find in stores after the flight. ( Airlines will not allow you to carry fuel in your baggage. )
I decided on a different approach this time. A compact wood-gas stove.
The principle is simple. Burning wood in the combustion chamber heats air which is then fed into the combustion chamber just above the flames which produces a very efficient burn.
A stove like this will provide useful heat for over half an hour on a small bundle of twigs, Nearly an hour on a handful of cut and split branches and if it is available, over a hour on a fill of eco cat litter.
Yes, that is not a typo... Cat litter...
I’m taking a slight gamble that the local supermarket will carry the type of eco. cat litter that is made from compressed saw dust.