I think V1's idea is good - except for the AVGAS. Make sure you know the situation 100% (well, whatever passes as 100% in these parts.....).
Lokichokio had AVGAS many years ago and I suspect they still do, as a lot of relief/humanitarian assistance flights into southern Sudan stage(d) through there.
One more thought about GPS - I have of course no idea of the installation in the a/c yo will fly, but if you plan on using a handheld, make sure you've got an external antenna! By which I mean an active antenna that plugs into the unit, but lives inside the cockpit under the windshield, thus having an unobstructed 'view' of the sky. Quite a few parts of Africa have rather poor satellite reception (not many satellites) and this makes all the difference! Costs a few quid/Euro/Dollars.