Want to know what's between Hong Kong and Macau? Water of course! About an hour's worth of it when taking a hydrofoil.
Besides the water you can see some interesting barely inhabited islands, shipping vessels, and of course other hydrofoils shipping people with money to lose to Macau, and people with empty pockets back (those that win at the casinos will probably spend a good chunk taking the chopper back).
What's the best way to kill time when going across? Well film the trip of course! At least that way you know you can bore everyone else with your video when you get back!