Please take as few big lenses, as you can. I think 100-400 with 7D for long distance will be enough.
Take 24-105 because it is all around lens for 5DIII, and 17-55 because of the same for 7D.
Remember 24-105 with 7d is 24x1.6=38.4 - 106x1.6=168 !
If one of them, camera or lens brokes, you can always have got the replacement.
At 19 or later it is getting dark. Your Sigma 35 1.4 lens will be perfect. It is a small lens, and not heavy.
Do not show you have got expensive camera, or big lens, when its dark, even on the main street.
Take your G15, it will be good for you, at those places. Try to take pictures without flash. With the flash you alert all people around.
Take extender 1.4x, just not for using it, but only if something wrong happens, and you have to combine it with 100-400 and 5DIII.
640mm (400 mm x 1.6) in your 7D is just the limit for hand-shooting i think.
On safari, If it seems to you, it is too far, do not take pictures. Ask the driver go closer. Tips can work miracles.
Your driver is worth 2 or 3 your big and expensive lenses.
Do not take any tripod. You can not use it in a car because of the crowd inside. Monopod sometimes can be usefull. But bean bag, or fleece sweatshirt in a shape of a ball will be much much better. In a car allways keep your camera straps on your neck, just not to lose your camera. Change lenses only when seating. Just to protect your lens falling out of the car. Much better is not to change lenses at all. Only in a hotel room. After day or two you will have the sand everywhere, in a pockets, in your bag, in your socs, pants, ears and eyes. The bag for the camera is important, but I have never found good enough for me. So I prefer the cheap ones and unobtrusive.
Take some plastic bags to wrap and protect your gear. There are storms in the middle of summer and you can have all your things get wet in your bag.
Take additional batteries for the camera, allways keep them fully charged (power failures). Small led torch will be usefull.
And the absolutely must have: binoculars. Animals generally are far far away, first you have to find them, reach them and then take pictures.
Do anything under the sun to see wildbeast crossing Mara river! Give up on baloon ride. It is expensive, boring and for old ladies, I think.
Too bad you do not take wide-angle lens. It is perfect for landscapes in Africa, but maybe your lenses will be enough.
I think one big lens is enough. Really. One man is taking pictures, the second one helps him by watching with binoculars. When the photographer will be bored and tired swap your gear.
summary: binoculars!,
5DIII, 7D, G15, batteries,
Sigma 35 1.4,
17-55
24-105
100-400
Have a good time.
and sorry for my english (not good enough)
