This is my kit - a cheap burner, £4.99 from supermarket, igniter, gas canister + stand, double skinned mug and aluminium pot.
It weighs just less than an empty 1 litre steel thermos flask.
In practice I usually leave it in the car for a welcome brew on my return. I'm with Andy and the chocolate - in poor conditions I just drink water and eat calories, no wish to faff about with hot drinks. Then again, I rarely stay on a summit for more than an hour, and rarely walk for more than a couple of hours each way.
It is arguably better than a flask, though, as the bits can be distributed around a tightly packed rucksack; the drink / food can be boiling hot; you can use a local water source.
The most interesting thing to me, was my discovery of Iso butane, which the Jetboil canister contains. Produced as a refrigerant to replace CFCs, it has a low boiling point. I can confirm that the stove works below 0c quite well, unlike "normal" butane / propane mix without pre-heat coils etc. I use the cheaper variety during summer