First of all, to enter South Africa you need to make sure there are two completely clean and unstamped pages in your passport otherwise even with a proper visa you may not be allowed in.  You also should have a photocopy of your passport stored in a separate, safe location in case you are a victim of pick pocketing so that entry out of the country does not become a problem.

Before heading out you must also present a vaccination from the yellow world health organization or be ready to receive the vaccination at the airport if you want to be able to continue into South Africa.  Medically speaking, it is important to also check with your insurance company before leaving for South Africa to make sure that you will be covered in the case that an emergency occurs while you are away.