Chapter 15 is an important elements of the storyas it reinforces one of the central themes of the novel: the power and importance of community and human generosity. The small diner is a microcosm for the larger world. Here, we see the wealthy customers come in and pretentiously complain about everything they encounter and leave little or nothing in the way of tips. We see the truck drivers who come in, are polite, thankful for what they receive, and leave tips for those that work there. But it is in the road-bound family (one much like the Joads) that we see the real push of the novel's message. We see the behavior of the cook defending and supporting the father's desire to buy a loaf of bread for his family, over the objections of the waitress. But then we see the transformation occur in the waitress when she sells the candy two for a penny. We learn after the family leaves that the candy really cost five cents each. This behavior is then reinforced and rewarded by the two truck drivers who witness the events leaving an extra large tip. This scene reinforces that tension between the classes and the power of generosity and community that is needed for the benefit of all.