So as you have realised, a visa is required for tourist purposes for citizens of Saudi Arabia visiting South Africa.
It depends a little on how thorough you want to be - but basically, the more prepared you are, the better chance you have.
For example, the most common documents cited as required include:
Passport valid for 6 months beyond date of departure.
2 passport-size photos with signature on reverse side.
1 completed application form (failure to complete the application fully and in detail may result in visa being delayed or refused).
Proof of sufficient funds to cover visit.
Onward/return ticket and, if in transit, proof of sufficient documentation for admission to the country of destination.
Extra ones that might be suggested include:
- No criminal record (if you have proof of this, it could be useful)
- Be of sound body and mind (hard to prove this though!)
- A plan describing your intent while in South Africa - where you're staying, what you want to do
- Evidence of hotels booked, car rentals and the like
- Contacts in case of emergency in South Africa (if you have any)
- A vaccination certificate
- Passport valid for no less than 30 days after the expiry of the intended visit.
- Proof of travel insurance / medical cover
Now the problem you have is most sites seem to say it can take 3-10 days to process. Of course as you travel a lot, you're probably aware that money can usually make these delays go away. Talk nicely to the embassy staff, ask if there's anything extra they might need, make sure all your documents are nicely organised, ask them about South Africa while talking - see if they're from there and if they have favourite places (makes a connection, meaning more chance of them helping you out).
