“The dawn came, but no day.” 

This is a description of the morning after a dust storm in Oklahoma. In a literal sense this refers to the way the sun’s light is dimmed by the resulting volume of dust still in the air. On a metaphorical level it alludes to the catastrophic nature of what has happened for the farmers.

“…sandwiches wrapped in waxed paper, white bread, pickle, cheese, Spam, a piece of pie branded like an engine part.”

This passage describes the lunch of the tractor driver. It is a substantial and more than adequate meal, especially given the hunger of the remaining people on the farms. However, the branded pie and wax paper suggests something artificial, mass-produced, and divorced from the land on which he is working.

“Got to think of my own kids. Three dollars a day, and it comes every day.” 

The tractor driver tries to justify his acceptance of the job. Even though his work results in the dispossession and misery of 20 families, it guarantees him a decent and reliable wage. He uses the dubious and selfish logic that the imperative to support his own family justifies this.