In the bushveld, nobody dresses up (except the English "county" set - poor things).
Most of the larger rest camps and private lodges have laundry facilities, which means you could probably get away with just two to three changes of clothes.
Avoid bright colours and white; neutral hues are best for game viewing and bird watching. Nights can be chilly, even bitterly cold in winter; pack a warm sweater, tracksuit or anorak.
Among other items in your luggage include a swimming costume, a sun hat, comfortable walking shoes and/or stout walking boots if planning a walking safari.
Personal toiletries apart from the obvious, should include a high (15 and above) sun protection cream, lip salve, good sunglasses, insect repellent, a small torch (fitted with new batteries and spares!), and enough binoculars to avoid a fight.
Field guides for bird, mammal and trees might be useful, but not essential as these may be available to purchase, in pocket form, or even "Tick-off lists" may be supplied by the lodge or camp. For definitive help and also advice on Malaria go to http://www.atlashealth.co.uk/