What do the gold coins the boy must scramble for at the battle royal turn out to be?

The unnamed narrator, the "Invisible Man" of the story has been invited to give his high school graduation address to the local townsfolk. Unfortunately, it turns out instead that he is simply a bit player in an evening of raucous entertainment for a baying mob of drunken white men.
After being forced to participate in a blindfolded boxing bout called a battle royal, the narrator is required to get down on his hands and knees and crawl upon an electrified rug for what he believes to be gold coins. It turns out that they are, in fact, worthless brass tokens.
The symbolism is inescapable. Gold is related to power, and as a young African American man in a deeply racist society the narrator doesn't have any. Despite jumping through so many proverbial hoops for the delectation of white people, he is still treated like dirt, reminded of his lowly position in a society that couldn't care less about him.