Early in the novel, The Man pries a Coke free from a drink machine. Although one critic has noted this was "perhaps the last can of Coke in the world" (source), The Boy and The Man do drink Cokes later in the bunker (221.1). Anyway, the can of Coke seems like an artifact from a former civilization – it might as well be the last Coke in the world.
On the outskirts of the city they came to a supermarket. [. . .] By the door were two softdrink machines that had been tilted over into the floor and opened with a prybar. Coins everywhere in the ash. He sat and ran his hand around the works of the gutted machines and in the second one it closed over a cold metal cylinder. He withdrew it slowly and sat looking at a Coca-Cola. (35.1)
The Coke can highlights a number of things for McCarthy: the deprivation of his characters (what kind of world doesn't have fizzy drinks?), the disintegration of consumer-capitalist society (read: America), and the magical quality of everyday things in this setting, not to mention a major generation gap.