Hello,
Went to SA with Vic Falls add on in August - you'll have the most fantastic time.
In SA I used a Rand cashcard and had no problems with this in shops or ATCs. I also took the full 5,000 in cash which was almost enough anyway.
In Zambia, the situation changed while we were there. Zambia now, officially, will only accept the Kwatcha which is a closed currency and can only be obtained whilst there. However, I didn't see a single kwatcha as the hotel accepts a rand or American dollar payment on a credit or debit card and the shop in the hotel accepts American dollars. almost everywhere else took either rand or dollar (including Botswana - a trip to recommended).
Therefore, if I were you, I would take:
1. a debit or credit card
2. a few American dollars (you will need 50 for your entry visa anyway, or 80 if you are doing the Botswana trip)
3. Sterling to pay for the optional excursions in Zambia (SA excursions are paid for, in cash, in rand)
4. A form of card (to use ATMs in SA) e.g. Rand Cashcard
5 The max of 5,ooo Rand in cash.
The downside of the holiday was the amopunt of cash we had to carry. Split it up for safety and use the safes in the hotels (almost all had one in the rooms which were easy to operate)
Hope this is a) clear, and b) helpful. I know it was one of the worries I had before I went but everything worked out ok and I had the time of my life - as I'm sure you will,
Regards,
Valerie