What are the most important symbols in chapter thirteen of The Catcher in the Rye, and what do they represent?

As the chapter opens, it's freezing, and Holden puts on his symbolic red cap:

I took my red hunting hat out of my pocket and put it on—I didn't give a damn how I looked.

The hat is his way of asserting he will be himself; it represents that he will not conform to social expectations. This cap signals what will happen, which is that Holden will exhibit his nonconformity by hiring a prostitute but only talking to her.
Another symbol in the chapter is the suitcase that Holden stumbles over as he answers the door to greet the prostitute, representing his desire for escape.
But the most important symbol of all is the prostitute herself. She is very young, a teenager about Holden's age. Even though she is hardened, she represents vulnerability, especially after she takes off her green dress. She is the kind of person Holden would like to protect, not sleep with.