Most Helpful Girl
Although it's summer it can get quite cold in the evenings in S. A it's also a bit dependent as to whether you'll be closer to say Cape town, Joburg or Pretoria.
So make sure to have at least one pair of pants and a warm jacket packed.
It also depends where you're from obviously and the temperatures you're used to.
For dressing I'd say just be yourself and dress the way you're most comfortable, your personality will impress her more than your clothes.
You'd be surprised no one remembers what you wear 2 or 3 days after except you, more so for men and boys.
Unless it's something extremely daring like a chicken suit.
Don't believe me? try to think about the clothes your siblings or parents or friends wore 3 days ago. Clothes are more of an extra oomph so just dress comfortable, naturally, avoid sloppy and you'll be fine.