A simple power-lifting exercise, the Bench Press, is excellent for improving chest muscle. However, CrossFit appears to prefer overhead rather than bench pressing, most likely due to the transition of overhead work to Olympic Lifting, but perhaps also due to the risk for having weak balance and rigid shoulders to perform too much bench work. Given the high degree of versatility needed in CrossFit skills such as Olympic Lifting and gymnastics, this may be counter-productive. But just make sure you combine some Bench work with a lot of back chain work.