Live in HK and all the above are good pointers, can even maybe loan you a bike if you fancy a cheeky trail though :)
As well as Big Wave and Repulse Bay can also recoemend Pui O on Lantau, get a ferry from central to Mui Wo and take a hike through Chi Ma Wan country park to it (couple of hours), you can get the bus back.
Bull Bike if your interested in some window shopping, they have 3 shops (general bikes stuff, Triathlete and Specialized) in Ya Mei Tei all within the same short street.
For eating local food, lots of places but I tend to go to Shim Sha Po, also home to one of the larger computer centres in HK (think tech bizarre).
When are you going, it might coincide with a festival or holiday, theres loads in the first part of the year?