What is the theme in Everlost by Neal Shusterman?

The idea of a coming of age theme in a story in which most of the characters are dead seems impossible but it isn't. Nick is a prime example of this theme though his maturity and self-confidence arrive as Nick is trapped in a pickle barrel. Nick is a natural complainer. When he and Allie are first awakened they believe they might have been thrown clear of the crash. Allie wants to climb back up the embankment and Nick agrees but is upset during the entire climb.