When Dexter is described as having caddied only for pocket money, it helps to illuminate his own financial condition. Dexter is relatively wealthy. Fitzgerald makes it clear that Dexter is not destitute growing up. The opening paragraph of the story contrasts Dexter's condition with the other caddies:
Some of the caddies were poor as sin and lived in one-room houses with a neurasthenic cow in the front yard, but Dexter Green's father owned the second best grocery-store in Black Bear--the best one was "The Hub," patronized by the wealthy people from Sherry Island--and Dexter caddied only for pocket-money.
Dexter was not poor, as he came from a relatively wealthy family. In caddying "only for pocket money," it helps to bring out why Dexter does caddy. He enjoys being able to be around the very wealthy and absorbing their patterns of behavior and their habits. For Dexter, caddying only provides the spare change that enables him to enjoy life. Yet, the real reason for his caddying is to bring him closer to the very wealthy, the individuals who embody the promises and possibilities of his "Winter Dreams."