If I want hot water fast, one of the best tools I’ve found is a device known as a Kelly kettle or volcano stove.
Apparently developed by Irish fishermen, a Kelly kettle is very simple: a vented pot into which a canister fits. The canister is a metal water jacket around a hollow shaft. One builds a fire in the pot so that water inside the jacket heats.
To operate, all one need do is uncork the reservoir of water and build a small fire in the pot. Prevailing breeze can be gauged with a glance at which way the smoke is blowing. The pot can then be turned until the vent is lined up with the wind, creating better draft. If the wind blows too hard, the draft can be turned away from the wind to adjust it to the right “sweet spot” to feed oxygen to the flames. The water boils very soon after, ready for a hot drink or to reconstitute dehydrated meals.
The fire chamber is small enough that any flammable fuel can work, even twigs, cones, and other pickings from the ground. This operation can be performed on any level, heat proof surface (I believe the Irish fishermen kept a little box of sand or gravel to set the kettle into for safe burning on board). Once the water is heated, removing the reservoir from the pot kills the draft, and the fire usually goes out almost immediately.
In the summer, when the weather’s pleasant, and too warm for the woodstove, we often boil water for morning drinks in our Kelly kettle. Getting out in the cool of the morning and making a small, fragrant fire of birch twigs can be a very pleasant way to start the day.
Kelly kettle manufacturers offer additional gear, such as grills, to expand the device’s cooking abilities beyond boiling water.