Who comes to see Atticus at the beginning of the movie? Why does Atticus tell Scout not to call for him next time?

In the beginning of the movie, a man named Mr. Cunningham brings some nuts for Atticus. Mr. Cunningham is embarrassed because he can only pay Atticus with nuts. Atticus does not want his clients, who are mostly all poor, to feel embarrassed about how they pay him for his services.