Some travelling tips: http://wikitravel.org/en/Hong_Kong
You can find groups of people with the same interests: http://www.meetup.com
Every Tuesday morning, there are flight tickets for low prices: http://www.cathaypacific.com/cx/en_HK/latest-offers/flights/fanfares/
Cheap flight tickets tips: http://www.reddit.com/r/travel/wiki/airfare
Flight ticket promos (in Chinese): http://flyagain.la
The most popular database of restaurants: http://www.openrice.com/
Sports courses, both short term (Uni-Adventure, e.g. two classes of sailing / surfing / diving) and long-term (Uni-Sports, semester-long): http://www.ihp.hku.hk
If you are in a group of 5 people in Sai Kung, it is cheaper, faster and more comfortable to take a taxi to HKU than to take minibuses and MTR.
LKF tips: Zinc has a happy hour until 10pm every day; Insomnia has free drinks on Tuesday nights after presenting a business card or liking their Facebook page or paying HKD100; women have free drinks on ladies’ nights in different bars: http://www.sassyhongkong.com/best-ladies-nights-in-hong-kong/
20 best happy hours: http://www.scmp.com/lifestyle/food-drink/article/1935715/20-hong-kongs-best-happy-hours-5pm-5am-and-hk1-drink
Feel free to add information about any interesting places, cheap air tickets, or University activities.