Almost anything you forget to bring along can be purchased inexpensively in Hong Kong. You won't be needing the winter woollies for most of the year due to the subtropical climate. The exception is from mid-December to February, when the tempature fall below 10c. But even in the summer, it is better bring along a light sweater, air-conditioning in some public transportations, restaurants and cinemas is often turned up high. Rain showers are possible during the rainy season around May to September,be sure to pack a light waterproof jacket.
What you need to pack depends on what you plan to do in Hong Kong. Swimwear for the beaches, stout shoes for pounding the sightseeing beat and smart casual wear for dinner are suggested. Formal suits are the norm for those visiting on business. Remember, Hong Kong is a shopping paradise, suggest to leave some space in your suitcase.