Although the 70-300mm f/4-5.6L is a great lens, it is pretty slow at its longest end. The shots of the jaguar at least, may occur in very low light levels where the f/2.8 would be an advantage.
You didn't mention if you are shooting with a full frame or a crop camera. If full frame, I suggest that you get a crop camera as a back up and as a second camera. If you are shooting with a crop camera, I suggest a full frame as a back up and second camera.
I would not go on a trip without a back up camera. Several years ago, I fell climbing a hill on the first day of a ten day trip to Alaska's Kenai Peninsula and broke my Canon 40D. The 30D I had as a back up and second camera saved the trip photographically.
I use a 1.4x TC with both my 100-400mm f/4.5-5.6L IS II and my 70-200mm f/4L IS lenses but, I understand that the 2x MK iii TC meshes quite well with the 70-200mm f/2.8 (series) lenses.
I would also bring a hotshoe flash equipped with a flash extender for fill light.