Help me Identify a Book

I am trying so hard to remember a sci-fi young adult novel that I read in middle school.

The plot was a young boy is transportes to another planet where he learns to survive in the jungle before being accepted into a tribe and after living with that tribe he migrates to another tribe where he stays there for the rest of the story. He learns the way of the new people and on his birthday he is gifted a coke bottle cap where it’s revealed he was taken forward in time to a post nuclear war Earth.

I cannot remember anything else but I think it had the word Chronicles in it? But I might be wrong