I made my way to Cuba with a simple mission—deliver one guitar to a music school there and see what happens. Eight years ago, I started a musical charity, Musack (musack.org), which provides instruments and supports kids’ music programs, after a rash of teen suicides hit my high school on the island of Nantucket. (Today, Musack is making music happen in Nantucket, Los Angeles, Compton, Haiti…