When attendees flock to BottleRock festival in Napa Valley, they aren't just paying to hear music. No, the $500 ticket comes with another perk: seeing their favorite musical acts cook, with everyone from shock rock legend Alice Cooper to Atlanta rapper Big Boi delivering dishes from center stage with celebrity chefs such as Padma Lakshmi and Trisha Yearwood.That's no coincidence. Food is driving festivals like never before.