Robben Island is a good day trip. So is the actual cape (of Good Hope), stop at Simonstown or one of the other coastal towns along the way for lunch. Watch out for the agressive baboons in the Cape national park.
Camps bay is a lovely spot for lunch or to stay. There are great wineries in striking distance. markets in Cape Town proper. The marina district is full of fun things to do.
Be aware that when climbing to the top of Table Mountain, there's a chance you may be robbed (or worse) especially at night - it's a notorious;y bad spot. Stick to the busier tourist parts. almost 5 years ago