If the online homemade crafts site Etsy were a documentary about musicians, it’d probably be something like “Big Easy Express.” This is the movie-watching equivalent of removing a screen-printed organic cotton cloth napkin from a hand-painted antique hutch and using it as a kerchief. I mean, it sounds fun being trapped on a moving train with Mumford & Sons, Edward Sharpe and the Magnetic Zeros, and the Old Crow Medicine Show. Each band practices a complementary variation of folk. Mumford & Sons, the most commercially popular, skew toward rock. Sharpe and the Zeros do ornate California bohemianism. And the Old Crow Medicine Show is a pleasingly smoky amalgam of country, bluegrass, and blues.