And make sure you buy a double bed sized mosquito net, better not to fall short. Donīt trust on the ones you saw on the lodge's video, most probably they will have holes on it; and you will have to overnight in an outstation which might not have them, sometimes.
Also take malaria pills with you at all times (the ones you take when you start feeling malaria symptoms, not the anti malaria treatment to prevent it, which can be worse than Malaria itself). In case you need medical attention ALWAYS look for a United Nations doctor (if there is any UN base at the place you are unlucky to fall sick in, of course). Try to avoid local "doctors" at all times (I have witnessed myself one of those "doctors" take a blood simple from a guy who clearly had malaria symptoms just to tell him to come back the next day (!!!) to check the results, while this guy was getting worse by the hour). If in doubt about malaria symptoms just take the pills, they can't do you any harm, anyway. Add a mosquito repellent for when you are outside at night. Do not drink local beers (if they have any).
Make sure there is a shovel in your airplane when flying during the wet season (April to November, approximately), you might have to dig your airplane out of the mud at more than one occasion.
During the dry season, after a windy day, visibility could be drastically reduced due dust suspended in the air for a couple of days, so make notes about obstacles at the fields you visit.
Always take dollars (euro is not welcomed in some african countries), and a good amount of small dollar bills in order not to get ripped off with the "I don't have change!" phrase. And of course, bills have to be recent (some countries require them to be not older than 1996, some others from 2000, etc.). I don't really remember if this was an issue in South Sudan; just ask your employer.
Appart from a couple of GPS's, the most important equipment for me is a sat phone, in case you have to do an off airport landing . Hope your employer provides you with one (make sure the battery is fully charged before leaving).