My wife and I were in Alaska for three weeks two years ago. We flew into Anchorage, but had the use of a friend's pickup all the time, so space and bulk weren't an issue. At the time I had a Zeiss 18mm f/3.5, but didn't use it much. I later sold the Zeiss and purchased the 16-35mm f/4 which is more versatile. Assuming you will find there is much more to shoot in Alaska than landscapes, here is what I brought. I always take two bodies that use common batteries and common memory cards. What if one breaks? At the time that was a 6D and a 60D, plus the Zeiss, a 24-105 F/4 L, 70-200mm f/4 L & 400mm f/5.6 L prime. There are lots of eagles in AK, and the 400mm was invaluable for raptors.
For this year's two week trip to London and Paris, as always I took two bodies for redundancy which this time were the 6D and 5DsR. Again common batteries and memory cards (plus compact flash for the 5DsR). In this case we were always walking and using mass transit (the Tube & buses), so weight and bulk were an issue. As it worked out I only carried the 6D and 24-105mm, while the other body and lenses stayed in the hotel. I would have liked to have had the 16-35mm in cathedrals and castles, but it just wasn't practical on this trip. My wife walks with a cane, so I couldn't weight her down with a bunch of camera equipment.
I am sure the 24-70mm is a great lens, but I am perfectly comfortable with a 6D and the 24-105mm for a walk around combo if I can carry only one body & lens. Indoors I shoot a lot at 6400 to 12,800 ISO, use the macro feature of the 24-105mm at times, plus enjoy its relatively wide zoom range. (You didn't say which FF body you have.)
If you go with the 16-35mm, I don't think the gap at 50mm is a big deal. On a four week car trip from Colorado to PEI in Canada, I took the kitchen sink and kept two bodies with lenses mounted all the time. Same when we were in Alaska. When you are driving you need to be prepared for what pops up now, not a few minutes later after you have fiddled with your kit.
