This is a good chapter to examine for its expression of the social values prevalent among the various different classes of people depicted in the novel.
The owner of the diner and the waitress who work there belong to the same social class as the truck drivers they favor. There is a kinship between these figures that comes from 1) the fact that the diner is created to serve the drivers and 2) the owner, waitress and drivers share things in common (income level, a sense of generosity).
The people who have more money and who look down on the first group are presented as being shallow, saddled with hubris, and petty (even criminal in petty ways). They complain. They steal. They are rude.
The final class of people depicted in this chapter is that of the migrant farmer (like the Joads). The people are humble, polite and destitute. They do not have much in common with the first class, except for a strong sense of decency. They do have something that both the other social classes seem to lack - a sense of honor.