Sal is an observer, I think this is something we have agreed upon. He exists to observe and to allow Kerouac to describe the setting in the way he wishes. Up to now, that is essentially Sal’s purpose in the novel. It's never explicitly stated but I think we can presume that Sal is human, and being a human he has desires... right? Doesn't he? He must... right?
Then what are they? What does Sal care about? I want to say he has a desire to write but it seems that staring at Dean is more important than writing. The only real interest he has shown is in women, and in showing that interest he tends to be a pretty sexist dude. Most recently we see Sal get close to Terry and jumps to saying that she is his, seeing as she is the girl he is closest to at the time. I could get in to how sexist Sal is in this instance in particular but I think I've explained my view that this is representative of the setting more than anything, and plus I think Meagan will have mentioned it for me already. The point here is that not only do I think Sal hasn't really been characterized enough, I barely consider him a character anymore. I see no motivations in him- no desire- nothing.
Anyways, I just wish the novel would spend less time “on the road” and more time in the character’s minds. Well no, in Dean’s mind, because Dean is all in this novel in comparison to Sal. The few hopes that I have left in Kerouac to make Sal a more interesting character are slowly beginning to shatter. In my opinion, it must be only a matter of time before Sal has some sort of experience that changes the novel entirely. I must admit, however, that I do enjoy watching Sal fail in becoming more like Dean. Other than being amusing, Sal’s character is just constantly getting wrecked for different reasons which is one of my favorite parts of the novel. I just want to jump to Dean so I can read about a bank robbery or some shit rather than the Adventures of Sal or Lack Thereof.