There are lot of 7-11 k-mart and other convenience stores at Hong Kong. When I visited HOng kong last year, I saw a few small supermarkets popping around the TST and mongkok.
I like to visit supermarket when I travelled because different countries have their different snacks and food. Moreover, the price is usually cheaper and is a good place to get gifts and interesting food.
This supermarket is one of my favourite. It is located at Tung Chung citygate outlet. It is like singapore hypermart.
Drop by if are visiting citygate at Tung Chung.