In the Path of Falling Objects — Andrew Smith

Jonah and his younger brother, Simon, are on their own. They set out to find what's left of their family, carrying between them ten dollars, a backpack full of dirty clothes, a notebook, and a stack of letters from their brother, who is serving a tour in Vietnam. And soon into their journey, they have a ride. With a man and a beautiful girl who may be in love with Jonah. Or Simon. Or both of them.

The man is crazy. The girl is desperate. This violent ride is only just beginning. And it will leave the brothers taking cover from hard truths about loyalty, love, and survival that crash into their lives.

One more thing: The brothers have a gun. They're going to need it.