-Take a jacket as it'll be cold at night and in the morning.
-Don't forget your chargers and a converter.
-Buy and bring an animal book if you'd like to know more about the animals you'll see.
-Get to know your driver(s) and guide(s) as you can become good friends. Ask them about the food the locals eat normally (like what the guides eat at home when they're not on safari), then request some during one of your many lodge meals. We did this and they brought us "ogali" with our dinner which was eye-opening and helped us understand the personal lives of the locals.
-Take single, dollar bills (lots of them!) to give as tips to the many people at each hotel /club who will serve you.
-Tip your drivers and guides when you are done.
-Ask them to teach you some Swahili then use it (Asante sana, hakuna mata, simba, pumba, rafiki...sound familiar?).
-Take some snacks in your luggage like candy, Powerbars, Cliff Bars, etc.
-Take a book or two to read and bring card games to play in down time if you like that sort of thing.
-Make sure you have sufficient SD cards...you'll take a billion pictures.
-Pack medicine like headache medicine, Ammonium AD(sp?), etc. as someone will get sick or get diarrhea for a day or two.
-If you want to buy souvenirs know that you'll see the same/similar carved figures, statutes, jewelry at most shops in the many stops you make.
-Try an African bottled soda or two while you're there.

Sorry for the lack of paragraphs! I've been over there twice and it's an incredible experience. There's so much more to see and learn beyond just the animals, so soak it in!