What role do the minor characters play in the novel Of Mice and Men?

The majority of the minor characters in Of Mice and Men play rather large roles in the story. Characters such as Curley's wife and Carlson are instrumental in moving the story along and demonstrating the beliefs of the particular time. 

Curley's wife is a good example of how women were viewed during the Great Depression era. It was a difficult time period, as both jobs and money were scarce. Curley's wife has dreams too, dreams that she shares about making it big, going to Hollywood, and starring in the movies. We never do learn her name though, despite the fact that her death drives George's decision to euthanize Lennie. Women fall into two categories in this text: "good" and "bad". We're really not given any examples of women who fall into the "good" category, with the possible exception of the girl whose dress is torn by Lennie in Weed. Despite her minor character status, Curley's wife is an instrumental and integral piece in understanding the thought processes of the main characters. 

Carlson is another minor character that is essential to understanding the text. He represents an "every man" type of character. He's the classic migrant worker, not too much of a thinker, not necessarily mean spirited, but definitely self-involved. Who isn't self-involved these days? It's the Great Depression and you've got to look after yourself. No one else will look out for you. Unless, of course, you're Lennie and George. That's part of what sets them apart. They've got each other. It's also what further illustrates the sadness of what George has to do in euthanizing Lennie at the end of the text. Carlson's thoughtlessness and lack of tact is demonstrated with how he behaves in the euthanization of Candy's dog and again at the end of the text in his behavior with George.