I have tinkered with my travel kit over the years, but now it's usually:
1. 5DIII + 24 1.4 II and/or 50 1.2; or
2. 5DIII + 24-70 2.8II; or
3. EOS M + 22 and/or 18-55IS
I remove my 5DIII grip as well, and I find that my travels rarely if ever require anything beyond 50 or 70mm and I've wasted lots of room and comfort carrying around my 135 2 (since sold), 70-200 4 IS (also sold), or 70-200 2.8 IS II over the years. I'll throw in my 85 1.2 II if I plan on taking lots of portraits (e.g. of family at Christmas), but that's the longest focal length I ever seem to need. I guess I like to get lots of context in my travel photos and find that I use 24mm 90% of the time for general shots and 50mm for most other shots, including people. I'm sure other destinations would really benefit from telephoto lengths, but this is what works for me.
I agree that for most travels, it's the shorter focal lengths that are most important, and a 2.8 zoom is the most versatile if you carry just one lens. I like being able to go extra wide or have more reach though.
In my vacation I often do a fast paced cross-country trip (ie fly-drive) and the flexibility of a zoom that includes a near-to-normal focal length is a must when there's no chance (or it would not be wise -dust/moisture) to change lenses. Hence there's some overlap in my zoom ranges. This is why I always carry the:
-17-40L for landscape/cityscape/sights. It goes wide and does the 'normal' 40 mm.
-24-105L for general purpose. I like the extended range - the 105 mm long end helps for subjects that are a little further away and I don't have much chance to get / or want to get too close to. And it's a 'normal' zoom.
-70-300 variable aperture lens for nature/tame wildlife, and of course for the compressed perspective. It does 70 mm too, which is quite usable as 'normal' (mildly tele) focal length.
-35f/2 or 50f/1.8: All my travel zooms are relatively 'slow' at a maximum aperture of f/4. Most of my photography when I travel is in daylight anyway, and I don't mind having plenty of DOF in most of my photos when I travel. Still, to make sure I have something to go to if I need a large aperture, the little 35 or 50 mm lens is there if I need it. I decide which of the two to take before I head off.
I am trying to get my mind around the 70-300 though; last year when I traveled through Turkey I didn't use it once. Though this time around we're going to Japan and I almost certainly want to have a good quality zoom with sufficient reach (that fits in my bag). Hence the 'L'
Of course I'm trying to justify this, I mean normally I don't really need such a lens as I also have the 70-200L IS f/2.8II, 1.4x II and a 100-400L. Yes- it's GAS I know.