For a few years now I always take a MSR Whisperlite camping stove for my walks less than a 1kg with the fuel it will boil a small kettle is about a minute. Your right there is nothing better than a proper cup of tea to keep you going on a 30 mile slog across Dartmoor Much better than a foul brew that has been stewing in a flask for a few hours.
That's a slick looking little device. Have to get me one. One can go without food for awhile, but drinking liquids is essential.