This is the first story , called "In the Box" from the collection of three stories called "Jack Glass" by Adam Roberts.
The antihero, Jac, is sent to a prison asteroid with six other prisoners. They are dumped on the asteroid with no resources at all except a box. It contains the absolute minimal material needed to survive on the asteroid. The prisoners, if they work together, can hollow out and pressurise a cave. Maybe. Or maybe they will die anyway. Those imprisoning them don't care. If the prisoners die it's no loss. If they manage to establish the start of a habitat on the asteroid, then they have done dangerous work, for free. Escape is impossible - they do not have enough equipment to build a spacecraft.
We are regularly told that they were given absolutely the minimal resources needed.
If they - or some of them - were still alive, then the Gongsi would recover them. ... Land a touch-up team, put in some windows, tow it into a more advantageous orbit, and sell it. ... And the prisoners? Released, ...
But first you had to survive the sentence. And that meant you had to turn a tiny pocket of air filling a declivity no larger than a room, near the surface of a frozen asteroid, into an environment that could support seven human beings for a decade and more.
But their captors have forgotten to consider that their bodies are also resources. The ruthless protagonist kills them all, and escapes by using their bodies as extra resources. The fat man is called Gordius.
"It's alright, Gordius," he called back, ..., "I'm ready for you now". ...
Afterwards, he brought the drills out of the tunnel and back into the main cavity. ...
He worked carefully, methodically, cutting open Gordius's corpse with as few and as small incisions as he could manage. He removed a great quantity of the innards. The skull came out once he had severed the spine and optical nerves, and felt his way around the cavity with his slippery fingers and long nails.
He packs the body with ice and the air scrubber (needed to breathe) and cannibalised bits from the other bodies. It is, to say the least, rather gory.