I think Holden’s hunting hat symbolizes his need to stand apart from everybody else. It’s like his way of saying “I’m not like any of you, phonies!”. He is so annoyed by the attitudes of other people that he just would not stand it if someone compared him to any other guy. He wears it a lot but I think he usually wears it when he feels he doesn’t fit in. Like the last day he was in Pencey, he wore that hat and he was so desperate to get out of there because he just didn’t belong there; he felt like a fish out of water.