Prescription Antibiotics: Should you get a form of infections and doctors may be out of reach.
Anti-diarrhea and Nausea Medicines: This is common and would recommend it. Also may be useful if a bad reaction to food or water.
Antihistamines: Allergic reactions can be common. This can be essential due to insect bites or food allergies.
Anti-malaria pills: Would recommend that one reads well on this topic. Some prophylactics e.g. Larium can have severe impact on the human system for some.
Antibacterial ointment/powder: Recommend in soap or liquid form. Important if going to be involved with physical activities e.g. Hiking
Painkillers: Most fuel stations in South Africa supply these in form of PANADO.

Travel Medical Insurance

Insurance cover for medical costs / hospital are critical and very important. Make sure you have your medical detail on hand always.

Would recommend only use private hospitals. Government hospitals are plagued with problems e.g.. Lack of staff or medicines. There are suitable Medi Centers that offer only doctor advice and medicine dispensary.

Familiarize yourself with where hospitals are in your environment.

Malaria

Malaria is not found in all the places in South Africa. Would recommend the following precaution rules in high risk areas:
RULE 1: Wear long pants and long-sleeved clothing. Critical times are especially around sun rise and sunset
RULE 2: Use insect repellents in form of cream and soaps.
RULE 3: If available use a mosquito net at night.
RULE 4: Spray your room before you go to sleep with Mosquito repellent and use accommodation with window $ door
RULE 5 : Request for Malaria test as soon as the following symptoms arise : chills, fevers, headache, nausea and vomiting.
See the Center for Disease Control web site for up to date information.

General Travel Safety

Petty theft is the most common crime you are likely to come across when visiting South Africa. Make sure you can see your belongings at all times. We would recommend that luggage has locks on. When traveling on airlines if possible plastic wrap your luggage to prevent theft and damage during transit.

Johannesburg is probably the most common city in South Africa for violent crimes e.g. car-jacking and murder. Wear a money belt under your clothing (to store travelers cheques, credit credit cards). In high risk areas don't wear watches or cameras around your neck. There are safes in most hotels, but are not always safe. Walking alone at night is not recommended. Would recommend purchase or hire of a GPS navigation system in order to assist travel and keeping in safe areas.

For further reading we recommend the following links:

http://www.adt.co.za/help/safety-tips.html
http://travel.state.gov/travel/cis_pa_tw/cis/cis_1008.html