Hi Jody,
Along with the good advice you have already gotten, you will find that most, if not all business establishments accept the major credit cards. Using your cards will also ensure you the best exchange rate. Check with your particular provider to see if they will charge you an extra fee for making international charges. Some companies do and some don't.
Many outfitters and some businesses accept U.S. cash and some even prefer it. Still, it's not a bad idea to get some Rand to have on hand. There are ATMs in all the major airports, and any ATM card within the Cirrus network will work. Also, the conversion rates at the ATMs are usually much better than the commission charged at the currency exchange kiosks. The only downside to the ATMs is that you are limited to $300 per day withdrawal.
I can't offer any shopping advice for Kimberley, but most outfitters are well aware of all of the good curio shopping in their area, and I'm sure they will allow for some opportunity for you to shop along they way. As a last resort, there is a massive gift shop in OR Tambo Airport in Jo'burg, called Out Of Africa. They actually have some very nice authentic art, curios, clothing, and jewelry at pretty good prices..... I don't know if your travels have you overnighting in Jo'burg at the Afton Guest House or not, but they also have an in-house gift shop and offer some really nice quality African themed jewelry... At least, that's what my wife says... Enjoy your safari!