A short story I read many years ago, I think Stephen King. Or was it Hitchcock? Have to search my old books. Two guys lost in desert miles from anywhere. They had just pulled off armed robbery or maybe murder for hire, can't remember but something bad. Had money but were out of gas.
Not much water, not enough to last for hours of walking. So they are getting fractious.
Survival of the fittest. One of them as I recall was trim and the other fat.
Car pulls into small town edge of desert, skipping, chugging, belching black smoke. Trim guy gets out. Car is junk but he has money for new one.
He had killed other guy, melted down his body fat and filled gas tank with it.