Strange - I replied to this earlier on but my post seems to have been deleted.
I used to live in that area and have fond memories of Hogsback. Take a MTB if you have one, there is good biking around there.
Kayaking wise - there is no decent river within a 100 km radius. There might be some obscure tributary that might flow after heavy rains but nothing that flows consistently.
Nearest river that flows all year round is the Fish River near Craddock which is part of an irrigation scheme and has some good sections on it (3 hour drive at least).
There is excellent surf all along that stretch of coast with great breaks around East London (Nahoon Reef, Gonubie, Yellowsands).
There are 2 rivers in the East London area (Nahoon and Gonubie Rivers) that are pretty good after heavy rains. Your best bet would be to contact some locals for details. Border Canoe Club has some kayakers in it but concentrate mainly on long distance K1 stuff.
Bigger rivers around are the Kei River (class 3) but I am unsure about access nowadays (unless you dont mind paddling from the bridge to the mouth - 80 km).
Another goodie is the Tsomo (class 4+). A great run but local knowledge is required. If you get an opportunity to get onto this drop everything and go. It has awesome playboating and some seriously steep stuff also.
Anymore questions fire away (bearing in mind I dont actually live there anymore).