Recently returned from 3 weeks in SA and Malawi. including 7 days on game drives, and we've been to the Kruger park in the past. Some thoughts that I hope are useful:
Dust is a real issue (take 2 bodies and don't change lenses while out on the vehicle); a lot of good shots on game drives are in the 50-100mm full-frame range; long lens requirements vary greatly according to which game park you're in.
Different countries & game parks have either open or closed vehicles - find out which you'll be using in advance. In an open vehicle handholding is usually the way to go IMHO, taking advantage of the back of seats etc if you can. To get good shots of animals reacting to you but before they run away (usually in in scrubby/forested parks) you have to be really quick, and I find beanbags and monopods just get in the way. In open vehicles you can often get nice and low, which gives a good perspective so you aren't looking down on the animals all the time (so generally I recommend sitting in the front row of seats close to the driver, rather than right up in the air on the back, which a lot of first-timers seem to like)
On the other hand if you are standing up and poking out of the top of closed vehicles in a big open game park then most people use beanbags, but I've not yet been to that sort of place.
This time I took only m4/3 mirrorless kit, partly because of advancing musculoskeletal frailties [!] but mainly because I wanted to combine 'travel' and 'wildlife' shooting with a light plane flight where the total baggage weight limit was 15kg.
I took 2 Olympus E-M1 bodies and Samyang 7.5 fisheye, Panasonic 12-35 f2.8, Oly 40-150 f2.8 and 1.4 converter and 45 f1.8 prime. I could have used longer reach than the FF 420mm gave, but not that often. With batteries, charger, cards, blower & other general hand baggage travel stuff this came to under 6kg in a LowePro 202 slingshot bag.
Focus peaking and manual focus was fantastically useful when the animals were peering through grasses and branches. I used variable ISO quite often, max 1600ASA which was just about OK early and late on the drives (but I hope for better from the "E-M1 II"). I'm not a bird photographer so didn't try BIF, but I did get some nice shots of birds on sticks and the ground.
If you're not on a specific photo safari, try to find a ranger who's keen on photography: I was really lucky in the Madikwe reserve in S Africa, where the guy we had understood very well what I was looking for, and I got some really nice contre jour shots & reflections (plus had good photo conversations, too).
Have fun!