It’s perfectly possible (and mostly safe) to rent your own vehicle and drive around yourself. A 4WD is a better option than a normal car (unless sticking only to the coast where there’s rarely a need for a 4x4.)
Keep in mind that driving conditions in East Africa can be a little hectic compared to what you might be used to and that it's normally cheaper - or the same price - to rent a vehicle with a local driver. This is the safer, easier way of doing it. They know the road conditions, speak the language and will often act as guide as well. They can watch your bags and the vehicle while you pop off to see something. Most people opt for a vehicle and driver rather than self-driving and it's what I would recommend.
