What to do on a layover in Hong Kong

I arrive in HKG on Cathay Pacific at 7.35am, then don't leave for Chiang Mai, Thailand, by Cathay Pacific, until 3.25pm. Firstly, do they transfer my luggage, and can I leave the airport to have a look around. If I can, what is close that I would have time to do, and allow me enough time to get back through customs, and meet my flight. If I can't leave, is there anything to do at HKIA so that I can stay awake. I'm on an overnight flight from Australia, so would rather be doing something, instead of sitting around.