Flamingo Vlei is on your right, which is a wetland area full of bird life. On Sundays you can pop into the car boot market in Milnerton or have lunch at one of the cafes next to the lighthouse at Milnerton Beach.
Blouberg Beach is a mecca for sea sport lovers. Kite surfing, windsurfing, stand up paddle surfing, regular surfing, if you can think of it, they are doing it. Maybe book a lesson before you head out? Use the words - Kite Surfing School - to find local teachers and equipment.
If you are after a bit more action, then keep the bike a day longer and do a spot of mountain biking. Downhill Adventures will show you the ropes.
And for those who prefer a more sedentary approach to sight seeing, don't forget the My CiTi bus heads out to Blouberg. You can get on an off as you wish.