This question usually arises while packing the bags and struggling with the luggage allowances. The answer is it depends, but in general it is not necessary. A monopod or beanbag are more practical and lighter for transport.
What zoom lens should I bring?
When shooting with a full frame camera at least a 400mm zoom lens is recommended. For DX format a 300mm lens is good. It will be multiplied with 1.5 and give even a slightly bigger zoom.
Do I need a wide-angle lens?
The zoom lens is more important, but it is great to have a wide-angle lens when photographing landscapes like in Namibia and on the Great Plains in Kenya and Tanzania. It depends very much on the destination.
Do I need a flash?
In general no. The flash usually does not travel far enough to have any affect, because the animal is too far away. It is also not nice for the animals to get flashed. And at night the rangers work with spotlights to shine on the animals (only animals that get not a blinding effect from the light).
Is a camera bag better than a backpack?
For transport a backpack is more practical, but on the game vehicle a camera bag is more convenient. It stands better in the vehicle and allows a more practical access to the equipment.