The poem is such an interesting one with Walt Whitman and Garcia Lorca in guest roles! He contracts with consumerism during his time and with Walt Whitman; who wrote the most patriotic and inspiring poems on America and its accepting unity and culture.

The supermarket is the symbolic America of Ginsberg. By deducing a large country into a small supermarket he put straightly what he intends to the readers: Consumerism. People Purchase things that they even don't know whether they want. We can see queerness-his own representation of his sexuality and how it is being affected in America through this poem. Modern American markets don't even know where the products came from. The poem is complicated in its themes.

Read Here: https://www.poetryfoundation.org/poems/47660/a-supermarket-in-california