The layering rule
Mornings are cold, midday is hot, and the wind can turn a beach day into a jacket day. Layers beat one heavy item. The Cape in summer is 15°C at dawn and 30°C by lunch; the Karoo in winter drops below freezing at night and hits 20°C by mid-afternoon. Pack for a 15-degree swing within a single day, and you've packed correctly.
Safari neutrals
Khaki, olive, brown, grey. Avoid black and white — black attracts tsetse flies in some reserves, white stands out and blinds wildlife — and bright blue (tsetse again, in parts of KZN). You don't need branded "safari clothes": any muted, breathable, long-sleeved shirt and trousers work. Closed shoes for game drives; you're getting in and out of the vehicle.
The sun
The UV is serious. Cape Town sits at 34° south but the ozone thins here, and burns happen fast. A hat you'll actually wear, SPF 50, and decent sunglasses are not optional — reapply. The sun you'll regret is the Table Mountain one at midday.
What you don't need
A massive first-aid kit (pharmacies are everywhere and excellent), a water purifier (tap water is safe and good), a plug adapter for every country (SA uses a large three-pin Type M, 230V — bring one, not five), or a sleeping bag (bedding is provided everywhere you'd sleep).
One thing to add
A small power bank — long game-drive days, poor signal that makes your phone work harder, and cold mornings drain a battery by lunchtime. And a light rain shell for the Cape winter, May to August, when a front can arrive in an hour.