I would highly recommend a drive out to Constantia Uitsig in Constantia, for lunch - about a 20 minute drive. Beautiful terrace and view of the vineyards/mountains, nice food, can only be in SA.

In CPT itself I'd recommend Wakame (good sea food, buzzy atmosphere), also Five Flies (more formal, restaurant is in lots of small rooms).

I think the best steak in CPT is served by the Nelson's Eye (in Gardens at the side of the Mt Nelson). Informal and slightly abrupt service, but GREAT steak. And amazingly good value.

And I second (third?) the previous recommendations of Codfather in Camps Bay. You can choose your own pieces of fish from the display (they do some meat as well). The grilled calamari is fabulous!