The board sport is most similar to surfing. Longboarding and skateboarding evolved from surfers wanting to ride waves on land. If your riding a longboard, carving and generally riding around will help improve balance, core strength, leg muscles and also be the closest recreation of moving a surfboard that you can get without water.
Lots of professional surfers also skateboard these days, practicing manoeuvres such as aerials on ramps before trying them in the surf. Skate parks with bowls, half pipes and quarter pipes are the best place for skateboarding if you want to skate with surfing style, with the shape of the ramp being the closest thing to a wave.