Sure you can do the hula! I've done hula on a couple vacations to Hawaii! ;) You can do just about anything you want as long as it's not high impact - no jumping or long distance running, for example. You can walk, hike, bike, do low impact aerobic exercise, yoga (carefully - certain positions you'll want to avoid), tai chi, swim, light weight training, etc. You'll probably be told not to lift anything heavier than 20 or 30 pounds, and to be careful to avoid falls.