If you are going to be photographing waterfalls, think about how you are going to get to an exposure of 1 to 3s to blur the water. You probably will need a 3 stop ND filter or maybe 6 stops if working on broad daylight.
If carrying a tripod is not an option, the you can shoot 1/6s to 1/4s hand held with the 24-105mm at 24mm fairly reliably. You may still need a ND filter to do that.
You may want to consider whether it is possible to carry something like a Gorillapod with, otherwise the approach I outlined above of using a wide angle lens with IS will help with photographing waterfalls.
Also think about taking a circular polariser.
I have to admit, I would probably make do with the 24-105 and 17-40. If I could take only one lens it would be the 24-105.
I spent last week in the Grampians and between my wife and myself we had a 5DII, 5DIII, 24-70 II, 24-105, 70-200 IS II, 17-40, 15mm fisheye, 50mm f/1.4 and 100mm L macro. The 24-70 and 24-105 saw most use. After that the 100mm macro and then we took a couple of shots with the 17-40 and 70-200. The fisheye and 50mm did not get used. We used a 3 stop ND for waterfalls and circular PL quite a bit. Our 10 stop ND did not see any use.