Moreover, for backpackers, you may have an idea that you can play around the city in the midnight, so I'm going to show you the stores that will open during midnight.
Some Chinese Hot Pot restaurants in Mong Kok and Jordan are opening till 4am or even 24 hours.
Some Bars, or lounges are opening till 5am too. If you are a soccer fans, you can go anyone of them for soccer games playing in midnight HK time.
Neway and California Red are two of the major chain karaoke box in Hong Kong. Most of their stores close at 5:45 am, you can hire a room and sing overnight.
7-Eleven and Circle K are two of the major chain convenience store in Hong Kong. Most of the stores are opening 24 hours (except those located in railway stations).
You may find any one of them near your hotel. You can go for a cup-noodle, hot coffee, sandwiches or anything, without paying for the expensive room service.
Some of the McDonalds and McCafe in Hong Kong are opening 24 hours. These shops will be displayed with a "24 Hours" label, so you can have hamburgers anytime. Moreover, the breakfast is served from 4 am, so you can have Hot Cakes since 4am. Some of these are equipped with pay TV to provide live soccer match broadcast.
Some Chinese Restaurant opens at 6am, so you can go to "Yum Cha" after the above stores closes.