The description of Crooks’s room is important because it does show a correlation between a man and his world.
Crooks is the only black farm hand at the ranch. This is the primary reason behind his keeping to himself, and for not being allowed to go and enjoy a game of cards with the other, white, farmhands. Aside from his race, Crooks is also mentally isolated from the others. He seems to use his bunk as the immediate habitat where he can be himself, kind of like a modern day "man-cave", colloquially speaking.
The state of his rooms, first and foremost, shows a level of personal comfort that many other farm hands have not achieved. This is because Crooks is the most "permanent" out of all the field hands, meaning that not only has he been there the longest, but that he obviously must have a strong tie with his boss. This is the reason why he allows himself to be a bit messy; he has acquired many, many objects (as a result of his permanence) through his years in Soledad, and perhaps having them laying around reminds him of his relatively good luck at the ranch.
....he was more permanent than the other men, and he had accumulated more possessions than he could carry on his own back.
Crooks also possessed books. This is significant because it shows that he is literate, perhaps even intellectual, considering that one of his books is a dilapidated "copy of the California civil code for 1905". Whether Crooks actually read that book, or whether he kept it in his room to give himself a sense of intellectuality is up to the reader to figure out.
The large amount of medical supplies that lay on his table also indicates that Crooks consistently faces the battles associated with being "a cripple", which also distances him from the other men. Surely, this is one of the main reasons why his attitude seems to be rotten half the time.
Furthermore, Crooks seems to be a natural collector of items that seem to have either come to him randomly or by second hand. Among these items there is a big clock (we are not told whether it works or not), a gun and, interestingly, a large shoe collection complete with boots! Not known for his fashionable style, Crooks seems to find some empowerment in collecting these items.
To the observer, it may seem as if Crooks feels that having these things gives him a sense of ownership and emancipation from the disenfranchisement that he suffers through the treatment of the other men, and because of his limited physical condition.
Hence, it is safe to conclude that Crooks is a man who has led quite a rough in life. As a reward for his life sacrifices, and for his permanence in the ranch, he has “awarded” himself the items that a man of means would have: shoes, an item of technological value (the alarm clock), a weapon (the shotgun), books (even if they are mauled and dilapidated) to create an atmosphere that would empower him within the overall atmosphere of the farm, itself.