Here would be my list:
1.) Use the moving sidewalks that are one level above the street in Central to explore the town a bit - they are less strenuous then simply walking and allow you to not have to deal with the traffic.
2.)Stop off at at the Dublin Jack for a late English breakfast.
3.) Check out the wet market - gotta love seeing all the crazy fish/animals that are still alive and and out for sale on the street.
4.)Make your way up to the Peak tram and go up Victoria peak to check out the view....its breathtaking.
5.)Take the Star Ferry over to Kowloon and wander around a bit (think the ferry costs $0.50 USD each way, roughly). The views of Hong Kong from the ferry are also breathtaking.
Hong Kong is a cool city. Unfortunately, I have only had 1 or 2 day stopovers myself, but these things are always fun to do. Lan Kwai Fong is the happening bar/club district if you want something to do at night. Wan Chai also has some good pubs but is a bit seedier.