How soon? You want to get everything you need for your shots. Odds are, you will be in the major metropolitan areas, and they are modern cities. But, you get 5 miles out of the city, and you are pretty 3rd world conditions in a lot of ways.

Others have said drink only boiled water. Part of me says pack plenty of water purification tabs, but if you are going there on business, don't let your local contacts see them. Serious insult. So long as you are in HK you should be OK. China is huge and poor and badly run, but thier enginneers aren't fools. And the Brits made a good system. If you want to be subtle, a waterbottle with a purifier/filter cap?

Carry with you exam gloves and 1st aid item; the stated sources aren't kidding when they say that EMS is almost nonexistant. Carry any meds you need on your person.

Carry your ticket, id, passport and all your visas (IIRC, you need an internal visa to cross from HK to the PRC proper) in a pick-proof manor. Maybe a travel wallet under your shirt and tie. Some people are saying cash, and it isn't a horrible idea, but I don't know what the current state of currency control is. If you bring in too much western currency, you might get hammered by thier cops.

Religous items are really, really twitchy. If you wear like a crucifix or a magan david, that should be ok, but documentation will make thier noses twitch. Remember, the state religion is Mao.

No knives, not even a micra or SAK classic. A low-to-medium flash light that runs on AA or AAA. Unless you smoke, nothing to light a fire with. We are talking seriously stripping out the kit, but remember that you are still talking about a repressive regieme that has serious paranoia issues when it comes to espionage and sabotage.

They will mostly looking at internal wreckers, but keep in mind that if you are doing anything terrifically important, or just look it, don't be suprised if you see the same person around you a lot- it will be your official tail. Take it as a compliment, they think you are impressive.

Take it for granted your hotel phone will be bugged. They might not listen, but they are probably recording. If you are bringing a laptop, talk to your IT guys about ghosting your machine before you leave, then formatting it and reinstalling just what you need. When you get back, have them save the items you need saved, then format the drive and put that old ghost back in. The local ISPs have some really spffy spyware that will want to give you. Among other things.

And whatever you do, don't act suspisious. YOur company won't be happy if you get PNGed or worse.

Wow, all the old paranoia and the rules to the games just came back. :P