A tramp (not the homeless variety) can do wonders for your snowboarding. Apart from the physical benefits and core strengthening it aids in improving your spatial awareness, adds muscle memory for certain tricks, and will help you to visualise the moves you want to do in the park.
Sessions on the trampoline will also do wonders for your upper body rotation and the timing of your pop. Many of the best snowboarders have a trampoline as an essential part of their training kit. Oh, it’s also a shedload of fun and sure beats a session in the gym.