Binoculars
This is not really a photography topic but I've included it anyway. Shooting pictures to take home is addictive and fun. But it's important to know when to put your camera down and just "watch" amazing interactions happen in Africa. Really cool stuff. Don't be the guy who always has his eye on the camera (look who's talking) or you will miss a lot of what being in Africa is about. ADS will have binoculars in the vehicle for you to use and they are pretty good. It also keeps you from having to carry that weight. But if you are really into observing the animals (and maybe aren't all that into photographing them) look into a pair of image stabilized binoculars before you go. They're pricey... but they are AWESOME. I have a pair of Canons.