About to turn the big 3-0, the country crooner took a step toward staying forever young by dropping a dress size. Her trick? Portion control. "I haven't given up everything!" the singer told PEOPLE. "I try to just cut everything in half." To stay fit on the road, Lambert now brings her trainer on tour with her. "We do cardio, a lot of circuit training. We do things with my body weight, like lunges," she says. And while Lambert didn't cut out the foods she loves, there was one thing that needed to go. "Just Cheetos mostly!" she says.