The cabin at Big Sur
The cabin at Big Sur is a symbol for self-examination. It's is supposed to be a place of relaxation and refreshment. Jack goes there to get his head straight again. Unfortunately, he learns that isolation only amplifies the internal dialogue. With all distractions removed, he still feels exactly as he did before. The solitude of the cabin only forces Jack to dive into the dark, ugly places in his brain.
"Willie"
Dave Wain's jeep "Willie" is a symbol for escapism. He deals with his issues by hopping behind the wheel. Unfortunately, he can't actually leave his problems behind. This is why his girlfriend and Rob travel around with him. They symbolize the futility of his escape. Even though he can put physical distance between himself and they things he fear or regrets, he still carries those things within his mind and memory.
Los Gatos
Los Gatos symbolizes the past, nostalgia. Jack and Cody drive there after Jack's first stay at Big Sur. On the way they discuss how the state of the country and their own lives are so inferior to how they were back in the day. They blame the government for most of their problems and society for the rest. As they drive toward Los Gatos, they're trying to drive back in time to when they felt more hopeful and confidant. Today they live with the results of their life choices of defying convention, but years ago they only had ambition and conviction to fuel them in their choices.
George Baso
Each of the characters of the novel are allegorical figures. They represents Kerouac and his friends, fellow Beats. George Baso is the clearest reference. He represents death. While he lies dying in a hospital from tuberculosis, he receives a visit from Jack and the gang. Upon seeing Baso lying there, Jack is overwhelmed by his fear of death and his dread of unavoidable mortality, yet he speaks of Baso hopefully. To Jack, if Baso can defeat TB, then maybe he can in turn defeat death.
Billie
Billie, like the others, is an allegorical character. She represents compromise. If Jack agrees to marry her as she wants, then he will abandon his convictions about nonconformity. Having devoted a lifetime to unconventionality and satisfying desire, he is struggling with the side-effects now later in life. Mortality is pressing in on him. Although he's in love with Billie, he doesn't believe his younger self would marry her. He desperately need to recapture who he was before all the inner turmoil, so he refuses to marry Billie now.
Cody
Cody represents idealism. He made basically identical life choices as Jack, but he isn't plagued with existential depression. When Jack is reunited with Cody, he desperately wants to explain to his friend all that has happened to him since their last meeting, but he can't seem to find the space in the conversation to do so. Cody has moved on. Jack is jealous that Cody appears to possess perfect confidence in his identity and no regrets about his choices. Maybe this is why Jack falls in love with both of Cody's women - Evelyn and Billie, - because he is jealous of Cody. By emulating Cody, Jack is hoping to rid himself of his mental distress.
