The Food in the Store
Notice that Faulkner never comes right out and tells us that Sarty is hungry. When we learn that Sarty's "stomach read" the cans of meat, we understand that he's hungry, and that he can't read the words, but only the symbols, the pictures of fish and the logo for deviled meat. The cans are also sealed. Sarty is hungry and he's surrounded by food. The problem is, the food is sealed off from him. It's a symbol of his general plight. He's constantly reaching for the joys of the world, but in large part due to his father's activities, these joys are sealed off from him.