Mosquito repellant and sunscreen.
Medicine for diarrhea. Check with CDC (Center for Disease Control) online about travel to East Africa.
No vaccine is required for Kenya, but prophylaxis for malaria is a must.
Luggage should be a wheeled piece weighing no more than 20 lbs when full and a carry on weighing about 8 lbs and not a suitcase. Laundry can be done everywhere on safari. Too much luggage makes for lack of space in the safari vehicle as well as while flying within East Africa in light aircrafts.
Bring a flashlight. Pack warm clothes such as a sweater or a parka with a hat and a swimming suit (camps and lodges have swimming pools). The parks being at high altitude, are cool in the mornings and evenings. Bring a good pair of walking shoes as well as water shoes or sandals (for the beach and seaside: as you may walk on corals, and would need protection from sea urchins). Bring an adapter to recharge your batteries, Kenya uses 220 voltage, the English system. In town, dress modestly.
Plan to change your currency into Kenyan Shilling upon arrival at the airport (it is difficult to change currency while on safari or the exchange rate may not be good).Visas are obtainable on arrival at the airport immigration services or online. Payment would have to be in dollars. Your passport must be valid for six months when you are ready to return to your country of origin.
Enjoy your safari!