Before Johnny dies, he has a brief exchange with Ponyboy. Johnny tells Ponyboy to "stay gold." Johnny is referencing the Robert Frost poem that Ponyboy read to him while the two boys were hiding out in the church. The poem, and its message, are important thematically to the boys and the book. An appropriate song would be Stevie Wonder's song titled "Stay Gold." Like the poem, the song laments the fact that nothing can ever stay perfect forever.
You thought that all would last forever
But like the weather
Nothing can ever . . . and be in time
"What I've Done" by Linkin Park would be another good choice. The song is about letting go and forgiving yourself in order to move on. Ponyboy is full of hurt by the end of the novel. Two very close friends of his are dead, and Ponyboy knows that he is a part of it all. In order to "stay gold," Ponyboy knows that he has to find a way to move on with his life.
I'll face myself to cross out what I've become
And let go of what I've done
Since the entire book is about two conflicting gangs, a song about gangs and rising above those challenges would be a good choice to represent Ponyboy or any other Greaser. Michael Jackson's "Beat It" is appropriate.
You have to show them that you're really not scared
You're playin' with your life, this ain't no truth or dare
During a conversation between Ponyboy and Cherry, she correctly explains a basic difference between the Socs and the Greasers. She tells Ponyboy that the Greasers fight because they feel too much, and the Socs fight because they don't feel at all. Nickelback has a song titled "If Everyone Cared" that I feel applies to the situation. The song says that if everybody felt and expressed emotions in a similar and loving way, then nobody would be killed because of emotional outbursts.
If everyone cared and nobody cried
If everyone loved and nobody lied
If everyone shared and swallowed their pride
Then we'd see the day when nobody died
By the final chapter, it's clear to readers that Ponyboy is in an emotional wasteland. He's barely functioning. His grades are slipping, he's depressed, and he is prone to emotional outbursts. He hurts badly. I think R.E.M.'s song "Everybody Hurts" is a good choice for this moment in Ponyboy's life.
When your day is long
And the night
The night is yours alone
When you're sure you've had enough
Of this life
Well hang on
Don't let yourself go
'Cause everybody cries
And everybody hurts sometimes