Will Kennicott can't be Sinclair Lewis's only example of a typical man in Gopher Prairie, so he throws in Sam Clark to remind us just how little diversity or creativity there is among these men.
Sam is one of the first people Carol meets when she arrives in Gopher Prairie, and her first impression of him is this: "The owner, now at the wheel, was the essence of decent self-satisfaction; a baldish, largish, level-eyed man, rugged of neck but sleek and round of face" (3.3.19). Like Will, Sam is your typical rugged man who likes to laugh at the same jokes over and over whenever he's not hunting or playing poker. He has absolutely no interest in high culture or any politics other than those of the Republican Party.
Even though he has no real interest in culture, Sam is more than happy to brag to his friends when he gets involved in one of Carol's acting projects: "Sam Clark had boastfully written about the dramatic association to his schoolmate, Percy Bresnahan, president of the Velvet Motor Company of Boston" (18.2.9). In this sense, Sam is just like anyone else in Gopher Prairie: he likes to appear cultured to other people, even though deep down, he has no interest in anything outside the usual interests of hunting and poker.
And sadly, this is pretty much what every guy in Gopher Prairie is like—at least as far as Carol is concerned.