There are limits on the amount of currency you can bring into South Africa. For cash in South African Rand (ZAR), the limit is 25,000ZAR. For combinations of cash in other currencies, the limit is US$10,000 (or equivalent). You should declare any amount higher than this on entry to South Africa.
There is a high incidence of credit card fraud and fraud involving ATMs. Make sure your PIN is not seen by others when withdrawing money from an ATM. Refuse offers of help from bystanders. Don’t change large sums of money in busy public areas.
Protect any documents containing details of credit cards or bank accounts.