You're allowed to bring goods of a certain value back home without having to pay duty or import tax. But there's a limit on the amount of tobacco and liquor you can bring back duty-free, and some countries have separate limits for perfumes; for exact figures, check with your customs department. When you shop abroad, save all your receipts, as customs inspectors may ask to see them along with the items you purchased. If the total value of your goods is more than the duty-free limit, you'll have to pay a tax (most often a flat percentage) on the value of everything beyond that limit.
Except for the usual prohibitions against endangered species, narcotics, explosives, firearms, and ammunition, and limits on alcohol, tobacco products, and perfume, you can bring anything you want into Hong Kong, including an unlimited amount of money. Visitors may bring in, duty-free, 19 cigarettes or 1 cigar or 25 grams of tobacco, and 1 liter of alcohol.