For a list of vegan foods in South Africa, like crisps, biscuits, marg etc check out this list.
http://www.vegansociety.co.za/index.php ... &Itemid=81
I just saw it recently and there are some surprises on there.
You can also get Cape of Good Hope's choc soy protein bars, the plain ones are definitely vegan and they have promised to remove the non-vegan D3 from their other bars this year so they are now possibly also vegan. Cape of Good Hope also do ice-cream and soya milk but you'll need to find the larger supermarkets to find the ice-cream's I suspect.
It's super easy to be vegan in South Africa, and I think Cape Town is probably way ahead of the rest of the country. Are you staying in a hotel or self-catering?