There is no such thing as bad weather. There are only bad clothes. But there are some genuinely bad roads in Southern Africa, not just bad drivers, and, short of driving a tank with very wide tracks (a surplus Russian T34, possibly) a 4x4 may offer the best solution. 

As always, try to limit the traces you leave behind - they say that in Namibia, tracks in the desert may last for 1000 years. But the journey should be as important as the arrival, and driving a 4X4 can often both make the arrival possible, and give many wonderful experiences along the way. A 4X4 can often be an excellent addition to an African trip - and for some places, it is less an addition, much more an essential.

What to take with you?

It is assumed that your vehicle is in good condition, and that you have adequate fuel until the next opportunity to fill up (it is important to confirm there will be fuel where you are headed - rarely, in Kruger, there have been problems - occasionally with a rationing system introduced, although this is very rare). Before worrying about contents, ensure that if you are going off the beaten-track someone knows where you are supposed to be heading for, if only as an insurance policy - so it is possible for the alarm to be raised if you attempt to disappear. Ensure that you have access to sufficient liquid - you would be surprised at the amount you will need to consume in areas of dry heat - many litres a day, especially if you are attempting to walk much. Some biltong - it also seems able to last for a few thousand years, if pushed - is also highly recommended (practically all South Africans and Namibians will be able to tell you where you can get proper, even lekker biltong, if you are lucky). Just be careful that as you feel your teeth gently break, you are able to persuade yourself that it is in a good cause, really.