Diner Scene
This scene makes me tear up every time. Grandpa only has a dime to spend on some bread. The waitress says that a loaf of bread costs 15 cents. Then the cook (I presume the owner of the diner) says sell it for 10 cents, even though they will run out before the next delivery. Then Grandpa asks about the price of some candy for the children. The waitress picks up on the owner's attitude and sells the candy, two for a penny (instead of 5 cents each). Grandpa seems oblivious. Then the two truck drivers, after watching all this, pay for their lunch and don't take their change. Their way of contributing.
While both the owner and the truck drivers are both gruff in their responses to the waitress (because they are "guys"), they are clearly sympathetic to the Joad's plight. I thought this scene was very well done. it speaks to the idea that some folks knew that that were lucky to have work. And only half-a-step ahead of the Joads. So they gave what they could. Very effective story-telling.