Start with what you think you should take ... then cut it by at least half! 

Do a bit of homework first about where you're headed

• What's the weather going to be like?
• What sort of places will you be staying in?
• Will they be likely to have laundry services, hairdryers, and so on?
• What sort of tours will you be going on? eg game safaris need very different gear to surfing safaris!
• Will you be going to nightclubs/upmarket dinners?
  

Here are some general tips that may simplify your packing ... and your travelling!

• Choose loose, comfortable cottons in natural colours eg khaki, light brown, olive.  They're comfortable to travel in and walk in and camouflage you well in game areas.
• Dress like an onion.  Layers work far better than one item of clothing.  Early mornings, late afternoons & night drives can be especially cold.  But then the midday can be bakingly hot.  You can't always go back to camp to change. 
• A small daypack/bag is great to keep shedded layers, your water bottle, sun-block, camera, hat & notebook & pen.
• South Africa is generally a fairly casual place, but more exclusive resorts may insist on dressing for dinner, with collar & tie for men & evening dresses for women. 
• Pack one smart outfit in the bottom of your bag/case - you'll never get caught out & you'll impress your fellow travellers no end.
• Always take a jersey/jacket if you're going out after dark.  Weather can be very changeable.
• Travel light!  Consciously think about where you can cut down on size or bulk eg just take the pages out of a guide book that you'll need - rather than the whole book.

Recommended clothing essentials: (quantities suggestions only)

2 Long pants
2 Shorts/skirts
2 Long-sleeved cotton shirts (double as sun-protectors & mozzie shields)
5 Cotton short-sleeved shirts and/or T-shirts
1 Light sweater/ sweatshirt
1 light windbreaker (waterproof)
1/2 pairs walking/hiking shoes (worn in!)
5 changes socks & underwear
1 hat with wide brim
Sunglasses
Swimming gear
Slip slops/thongs/jandals - great for beaches - and dodgy showers

Vital : 1 x kikoi/sarong - cotton wrap that can be used as a scarf, towel, beach wrap, table cloth, hammock, pillow, turban, sheet and, and, and  ...

Recommended medical/personal supplies:

• Insect repellant (good one, containing DEET) eg Tabard, Peaceful Sleep.  Lotion/spray works best.
• Small first aid kit with plasters, pain killers, moisturiser, lip balm, anti-diarrhoeal tablets, anti-histamine cream & tablets, general antiseptic cream, needles, prescription meds (and a prescription refill if you'll be needing it), condoms Excellent sunscreen - SPF 30 or higherSewing/repair kit: needles & cotton, nylon string, duct tape.
• Plastic zip-lock bags in various sizes
• Use travel-sized bottles rather than huge bottles - you can always refill as you go.
• Swiss Army knife (pack it in the hold - won't be allowed in your hand-luggage on flights) - you never know when you'll need to open a bottle of excellent South African red!
  

Extras to consider:

• Spare camera film/memory card
• Spare batteries
• Good small torch
• Good small binoculars
• Gloves & beany (for really cold nights and night game drives)
• Down vest/jacket if you feel the cold & you're visiting in winter

Vital checklist:

• Passport with at least 4 empty pages & valid for at least 6 months. 
• Leave photocopies of your passport, travellers cheque numbers, driver's licence and any other NB documents with a close friend or relative who can get them to you quickly in an emergency.
• Valid visa (if needed)
• Spare ID photo
• Travel insurance - don't leave home without this!
• Positive friendly attitude - the best thing you'll ever pack ... or need!

Packing tip: rolling up your clothes seems to crease them less than normal folding.
 

Quite a fun resource that custom designs your packing list for you depending on your sex, time of year, min & max temperatures, interests, activities and so on is http://upl.codeq.info/index.jsp