Hey, there! I too am looking forward to marching in a corps this next season. I march snare, but am an avid weight lifter, and it has REALLY helped me out in every aspect of marching, and even my life. As I stated before, I play snare however, by the way I see that contras hold their horns I would imagine that some solid shoulders would come in handy. My favorite exercises for shoulders are military shoulder press, and lateral shoulder raises. This has dramatically increased the size and strength of my deltoids (side of shoulder) and posterior deltoid (back of shoulder). Hope this helps! Best of luck to you! if you have any questions, send me a message!