The books are an indication that Crooks, unlike most black people in California at this time, has some education. He has a copy of the California Civil Code, showing that he understands his rights in the state. His “gold-rimmed spectacles” also symbolize his intelligence. The “dirty books” are evidence of isolation and loneliness – the only female company he can expect on the ranch is in pornography. The bottles of liniment reinforce the reality of his disability, and mean he is one of the “weak ones” Curley’s Wife refers to.
It is important to see that Crooks sleeps on a bed of straw – he is treated no better than an animal in this regard. It reveals his status on the ranch as a black man.