"Readers do not learn Sammy's name until the end of the story, even though he is the first-person narrator of the story. He is a checkout clerk at an A & P supermarket. His language indicates that, at age nineteen, he is both cynical and romantic."
Sammy starts the story as a silly boy completely disassociated with his environment, the store, it acts as a source of entertainment for his cynical sense of humor. Once the girls enter the store, Sammy's interest is peaked, and he decides that he wants to get their attention. To do this, he takes a stand against his boss, who has informed the girls that they are not dressed properly for the store.
Sammy decides to be a hero, hoping to impress the girls who are leaving the store. His strategy fails, the girls do not notice him. He has quit his job for nothing. Now he has to deal with the consequences to his life.
Sammy's character is not fully revealed in the story. In fact, the reader knows only what goes on in the store with regard to Sammy's life. His behavior in the story suggests that he is immature and irresponsible. Even though, at the end of the story, it appears that he becomes more reflective.
"His face was dark gray and his back stiff, as if he'd just had an injection of iron, and my stomach kind of fell as I felt how hard the world was going to be to me hereafter." (Updike)