Wherever you arrive in South Africa, there will be a customs control. You will have to complete a "Traveller Card" where you declare any goods you may have and perhaps make a verbal declaration. To avoid a fine, you need to know what you must declare.
South Africa accepts restricted quantities of certain consumer items, that you can bring into or out of the country without incurring import duty or VAT. Here is the list: up to 200 cigarettes and 20 cigars per person, 50 ml of perfume and 250 ml of eau de toilette. For wine, (and it is good in South Africa, don't deprive yourself!) you can carry 2 litres, for other spirits and alcohol, the limit is 1 litre per person. Under 18s also have this allowance except for tobacco and alcohol.
You can bring one month's supply of medicines for personal use. For a longer period, you need to bring a current prescription or a doctor's letter and make a declaration. Other goods must be for personal use and non commercial. For very expensive goods, you may be required to pay a deposit which will be returned to you when you leave the country.
You will have to pay customs duty and VAT. Up to a value of 20,000 Rands, you will need to pay a flat-rate customs duty of 20% which is exempt from VAT, once per person for a period of a month. Above this limit, duty will be applied to each item individually and will incur VAT at 14%. Goods for commercial purposes, firearms and goods or items carried on behalf of others do not qualify for the flat-rate duty.
You must declare all currency above the limit of 25,000 Rands in South African banknotes and above the limit of 10,000 $ US for any other currency, as well as gold coins, coin and stamp collections and solid gold. You must also declare any firearms (authorised only if you have a permit), any plants or animals, dead or alive, belonging to an endangered species, and any product derived from them, any biological product (including vegetable oil and margarine) and any live animal.
It is illegal to bring into South Africa any drug or medicine forbidden by the State, any toxic substance, any product contravening the law (counterfeit), and contraband cigarettes.