This short story definitely contains solid examples of symbolism in it. The clothing worn by characters is a good place to start. For the most part, I would assume that the standard clothing worn by most of Sammy's customers identifies them as boring housewives. The three young girls that walk in immediately stand out to Sammy because they are not wearing the standard A&P clothing. They are wearing the complete opposite: they are wearing swimsuits to a grocery store that is not exactly right next to the beach. The bathing suits are symbolic of their youth and energy. They are exciting and fresh for Sammy and Stokesie alike. The clothing as a symbol is especially important when analyzing Sammy. He is an employee, so he is dressed like one. He wears his apron to be identified as a member of the establishment. That is why it is such a big deal that he takes it off.
I pull the bow at the back of my apron and start shrugging it off my shoulders. A couple customers that had been heading for my slot begin to knock against each other, like scared pigs in a chute.
He is quitting his job, and the act of taking off that article of clothing makes his actions quite concrete and visible. The act is so strong and symbolic that the customers in the store do not quite know what to do with themselves. They are once again compared to simple farm animals. Sammy repeatedly does this to the customers. He never once refers to them as any animals that would be classified as regal. It is always a dumb animal like a sheep, and that is symbolic of his attitude toward the customers.
A final symbol in the story is the herring snacks that Queenie buys. The snacks are symbolic of Queenie's wealth. She is rich and comes from a rich family. Updike could have had her buy anything in this entire grocery store, but she buys a fancy snack. Sammy picks up on that clue. He imagines being at a party with her surrounded by fancy rich people.
All of a sudden I slid right down her voice into her living room. Her father and the other men were standing around in ice-cream coats and bow ties and the women were in sandals picking up herring snacks on toothpicks off a big plate and they were all holding drinks the color of water with olives and sprigs of mint in them.
He contrasts this with his own family parties and tells readers that his family's idea of fancy is stenciled beer glasses.