While assonance appears throughout "The Bean Eaters," it's densest in the opening stanza. Take a look at the first line:
They eat beans mostly, this old yellow pair.
Assonance emphasizes long /ee/ and /oh/ sounds, encouraging the reader to linger on this image of a worn-out old couple huddled over their beans. The long /ayr/ sounds of "pair," “affair," "chipware," and "flatware" do similar work, drawing attention to the simplicity of the couple's meal and the cheapness of their utensils, highlighting their poverty.
In the following stanza, long /oo/ sounds create internal rhymes:
Two who are Mostly Good.
Two who have lived their day,
Here, assonance calls attention to the anaphora of “Two who," and creates a feeling that this old couple are so used to each other that they just about "rhyme" themselves.
The poem’s final long line is a list of the many items that jog the couple’s memories:
As they lean over the beans in their rented back room that is full of beads and receipts and dolls and cloths, tobacco crumbs, vases and fringes.
The /ee/ and assonance here is both musical and meaningful: those repeated vowel sounds fall pleasantly on the ear, but they also subtly evoke the monotony of the couple’s routines and the heaps of mementos they live in.