Nothing spectacular, it is only a two hour flight after all! Most (if not all?) of the preflight perks you would get with your BA Silver anyway.
Check-in: Dedicated Club Check-in
Lounge Access: You can use the Slow Lounge. Great Lounge, but can often get very full due to all of the FNB customers floating around in it.
Priority Boarding: Have never seen this work all that well on a South African flight. Rather spend a few extra minutes in the lounge.
On the plane: Basically just a slightly nicer than economy service. Bigger seats, pre-takeoff drink. Steel cutlery (apposed to the plastic that is sometimes used in the back!)

Have fun!