Chill on the beach
There are many good beaches to choose from and you can surely find one that suits you. repulse bay is the biggest and most popular beach and is suitable for families with small children. big wave bay is popular with surfers. shek o attracts a young chinese crowd, especially older teenagers and young adults. middle bay is popular with gay men and is a 20 minute walk along the coast from repulse bay. south bay beach is never too busy, even on weekends, but you will need to take a taxi from repulse bay.
Hiking
Walk the dragons back. take the number 9 bus from shau kei wan mtr station, to just after the small roundabout at tai tam gap. walk up the steps by the "shek-o country park" sign and turn right along the hong kong trail.