The first few days in Hong Kong it rained a lot. Despite the rain, the heat and humidity were high. One item of kit I would recommend is an umbrella, everyone in HK uses an umbrella instead of raincoats and with the heat, I can understand why.
I spent my time exploring some of the areas around Central and a few of the shopping malls. The IFC is the financial centre of HK and the mall had several floors of shops, cafes and restaurants. It is a great place to hang out if you need some air conditioning. The shops in IFC are not that great unless you are loaded, it reminds me of an airport lounge in that respect; a typical row of shops on IFC might be Versace, Tiffanys, Burberry, Conrad, Cartier... you get the picture. I did find a reasonable book shop, I think it was called "Page One".
Festival Mall is much better for normal shopping, this is a bit of an MTR journey from Central, but if you have your Oyster card it is no big deal. If you are into bookshops, this had a huge bookshop (Page One again I think).