Traveling can be stressful and, even if you are careful, robberies can happen. It is possible to avoid some problems by considering a guided tour or using public transport.
Through Kenya e-Citizen, you can create an account to pay your entrance fee to all national parks and many of the government-run museums and other cultural attractions.
Many places don't accept cards, so always be prepared with at least a little cash on hand. But be careful when carrying cash.
Anything vaguely touristy in Kenya is quite expensive. A ticket to a national park can cost 50 dollars.