We would suggest that you don't. Kenya, while a heavily trafficked country with millions of tourists every year, is still a third world country. The roads are bad and dangerous, the police might not always be there to help you and the culture is nothing like you are used to. We suggest that you go with a group or guide, someone who has your safety in mind. Sure, you can walk around Nairobi for the afternoon alone or go to Mombasa alone, but we would highly recommend that you not rent a car by yourself and take off into the bush on your own "wild safari." Obviously the same goes for hitch hiking. It might be a warm climate and seem friendly enough but, in the end, you are in a very very foreign land and one that does not have the basic security of a first world country.