I think that you have two approaches to this. You can derive music that is inspired from your reading of Just's novel. In this light, no one can help you because it will be based on your own inspiration. To another extent, you can identify certain patterns and ideas from the story and match them up with songs. This is where more help from outside sources can be offered. I can help out to an extent. You might want to cross check some of these songs featured with how you feel about them. An assignment that calls for a soundtrack should never be assembled if one does not like the songs.
1. "Like a Rolling Stone" by Bob Dylan- This song speaks to a rootlessness and a wandering throughout life. There is a selfishness presented in the song to those who move from place to place, relationship to relationship, and interact with the world in a rootless sort of way. Certainly, this idea of not having roots is something that applies to Sidney and Angela, who see themselves as "citizens of the world" and do not hold national identity to be important.
2. "Money for Nothing" by Dire Straits- Just's depiction of America as a consumerist nations that is immersed in self- absorption is seen in Angela's father. This song speaks really well to the results of a consumerist culture and its title might reflect how Carroll's making of money and work ethic might be represented.
3. "You Know That I'm No Good" by Amy Winehouse- It is a sentimental chocie with her recent passing, but the manner in which America is depicted in the novel is one where nearly every European understands what America is and how America is perceived. It might be a nice song to work into this dynamic.