I saw you, Walt Whitman, childless, lonely old grubber, poking among the meats in the refrigerator and eyeing the grocery boys. I heard you asking questions of each: Who killed the pork chops? What price bananas? Are you my Angel?
The speaker now imagines that Whitman is in the grocery store with him. Whitman has left his imagination and entered the store itself. Sort of.
Unlike the families who shop together, Whitman is all alone. And the speaker imagines that he's lonely. He's also childless—another hint that the speaker may be positioning himself as Whitman's poetic heir, or son.
He imagines that Whitman is "eyeing" the male grocery clerks. He's not hitting on them; he's just checking out the goods, and at the same time, suggestively checking out the meat for sale. Are the grocery boys for sale as much as the meat is for sale? Who knows? But our speaker is definitely imagining that they are.
The speaker imagines that Whitman asks the grocery boys questions. He mentions bananas, which seem, once again, to be sexually suggestive (or maybe it's just us).
Is Whitman isolated because of his sexuality? Is Garcia Lorca? Is the speaker? Do they not have wives and babies to shop with because they're gay? "Supermarket" doesn't answer this question, but it definitely poses it for us to think about.
Whitman's last question to the grocery boys is: "Are you my Angel?" It sounds like Whitman is looking for more than a sexual connection. He's looking for something heavenly. But the speaker never imagines a response from the supermarket clerks, so the question is left hanging in the air. Bummer, right?
I wandered in and out of the brilliant stacks of cans following you, and followed in my imagination by the store detective. We strode down the open corridors together in our solitary fancy tasting artichokes, possessing every frozen delicacy, and never passing the cashier.
Our speaker keeps on imagining that Whitman is in the supermarket with him. Now he's following Whitman through the "brilliant stacks of cans."
But he imagines that the store detective is hunting them down. Why? Have they done something wrong? Is there even such a thing as a "store detective" anyway?
We find out in the next line that (in the speaker's imagination), he and Whitman are sampling the food in the store without paying for it. They taste the artichokes. They "possess" (quite a strong word if you ask us) the frozen foods. They never pass the cashier, so we can infer that they don't pay for any of their tastings. Or to be more blunt: they are stealing food. Maybe they do deserve to be tailed by that store detective! Or maybe the speaker's being paranoid.
One other important thing: the speaker tells us that they walk through the supermarket "together in [their] solitary fancy." It's kind of a weird statement. Why are they solitary? They have each other, right?
Maybe there's a recognition here that the speaker is still lonely, even after he's conjured up his imaginary friend Walt Whitman. And maybe even the imagined Walt is lonely, too. But at least they're lonely together.