Shopping: Several outdoor stores sell caving equipment. Most of it is quite expensive. Sham Shui Po has batteries, chargers, led's, and all manner of other useful electronic parts.
There are some mines in Hong Kong.
Mt. Davis Youth Hostel: Clean and cheap, this is a much nicer place to stay than Mirador Mansions, but it's a bit inconvenient if you're heavily laden with baggage.
Money in Hong Kong is no problem whatsoever. Almost all the cash machines will take Cirrus cards etc and you can change money all over the place, including into RMB (maybe not at the airport but certainly in town) which is probably worth doing since it's bound to be at a better rate than you'll get with anything involving a credit card in China. If your card doesn't work in the first cashpoint you try, try it at a larger, more well-known bank such as HSBC. In Mong Kok there are several vendors which exchange RMB and HKD at good rates. Avoid exchanging on Nathan Road.
Provia available from Citicall.
Internet access is expensive in net bars, free in the library.
A HK city map will help you out no end, you'll probably be handed a perfectly usable free one just after you clear immigration and customs on landing. If not then you can buy a more detailed map from the newsagents in the airport. The map in the Lonely Planet guide isn't detailed enough to be of much help.
Visa issued free on arrival.
Buy a phone card to save money. Octopus cards work in some phones.
Loads of 'em.
From Hong Kong there are a variety of ways to enter the mainland. By far the fastest and easiet is just to go directly from your air-conditioned international flight, to your air-conditioned internal flight, only despite the fact that Hong Kong is technically a part of China these days, you still get to pay international departure tax. Gotta love it. You can avoid international tax and bring the price of your ticket down substantially by hoping the border to Shenzen and flying from there.
Getting around in Hong Kong is no more or less difficult than getting around say London. From the airport the bus is a significantly cheaper way (about a third the price) of getting into town than the express rail link is and is just as comfortable and easy (apparently there's a free shuttle bus from one of the express rail stations to the ferry terminal though). You'll need to make your way to the China / Hong Kong Ferry Terminal on Canton Road in Kowloon. Like most buildings in Hong Kong, the ferry terminal is slightly disguised as a shopping centre so don't just walk past it ! It's easy walking distance with gear from either Tsimshatsui MTR (underground) station on Nathan road (which airport bus A21 stops near) and also from the Star Ferry Terminal (easy to get to by bus from anywhere and signposted on foot). If you overshoot on the airport bus or decide to spend a night in Hong Kong then making your way back to one of these should be dead easy by either MTR or bus. The key to local transport in Hong Kong is an Octopus card. You can use them on the buses, MTR, some taxis, some minibuses, some ferries, etc. You can buy an Octopus card in most MTR stations.