Jade
from Jade Market or Cat Street Market, don't forget to bargain, usually you can get it for half of the price
Traditional Straw Hat
from Stanley Market, less than 100 bucks.
Fake Watches
From Ladies' Market or Temple Street Night Market. Make sure you don't pay more than 400-500 HK$ for a watch. The price depends on the quality, Grade A is the most expensive. But who can tell if it's really grade A...
Cameras
Souvenirs