Consider getting your visa before you go: the process is simple enough at Nairobi airport, but if you choose the wrong queue it can take over an hour, and it's the last thing you need after a long flight. We stood and watched people with pre-bought visas walk straight through passport control- we finally joined our group after over an hour.... we were last out of the airport!
Consider getting the flights yourself: we have done three trips with Exodus now, and we have had considerable difficulties with ensuring seating together on every single trip- despite assurrances that we have got seats booked together on the plane. It may not be an important part of the trip for you, so forget about it, but it's important to me to sit with my husband, particularly on night flights. We have had to battle with every check in that we have done to try to get seats together- it baffles me that people booking together as Mr and Mrs would be separated but, go figure! We were finally seated together on this trip after some juggling at check in, to find we had been separated again by the time we got to the gate! I will definitely travel with Exodus again, but I will be booking the flights myself.
On a supermarket stop for water, get some snacks for the road trip from Elementaita to Masai Mara and have them for your packed lunch- the packed lunch provided was over priced for what was a box of left overs.