I have three brew kits, bits get swapped and changed but they are different sizes. My usual is the swedish trangia, great for in my bergen and everyday "normal" use. My second is a lightweight aluminium cookset, two pans and a lid, with a folding cup and sachets of coffee, sugar and little "maccy D" milk cartons (they are good for a few months) along with a few hexy blocks, standing on a couple of stones like wayland, and this lives in my bumbag. My third is usually in my smallish metal mug(not crusader size normal mug size) with sachets and a couple of BBQ matches to use to heat it, this can sit in my jacket pocket, but is usually in my handDitch the stove and wrap the hexi tablets individually in foil.
All you need then are three pebbles to stand your metal cup on, unwrap the tablet and burn it on the foil. When cup is boiled, blow out the tablet and re-wrap the remains.
I can usually get two boils from a good hexi tablet.
The hexy and BBQ matches are a bit messy to use but are great for an emergency, completely fool proof, no getting out a stove and finding you have run out of fuel when you need it most
The usual problem I have is carrying enough water, but I have a millbank bag in my bumbag too, so in an emergency I am sorted.