Chapters 1-5 Response:

Holden's red hat basically just shows that he is different from other. He always says when he is wearing it. He never seems to wear it when he is going to be around people that he knows. The color of it is red just like his brother, Allie, hair was.
Holden seems to separate himself from everyone else. He doesn't go to the biggest game of the year. He seems to like to be alone most of the time. He seems to want to do what he wants when he wants and he really doesn't care what happens.