Khaki cotton/linen longs, good socks, white or khaki shirts with space for bars. Light yet comfortable footwear is a must. Don't go too Rambo on the desert boots. Blundstones are good or pick up a pair of the local Jim Greens in SA. Look at boxers rather than briefs as the heat and humidity can cause quite a severe dhobi itch if you wear the wrong kit. The khaki stuff and other clothing is all available in SA if you want to stock up here and save weight/space for a few luxuries from home.
Might find your aircraft space/weight limited as far as the med kit and grab bag goes. The Yanqui turistas in the Delta carry a lot of baggage. Keep it small and it may be a good selling point if you're seeking work but don't be surprised if they're actually looking for pilots. Bring a spare liver if you're heading for Maun.