Tried all kinds of combi, thought I should share my exp. Weight is of utmost importance for travel so I try to take minimal gear (that I can manage comfortably. YMMV)
-----All Prime-------
35mm 1.4 sig, 50mm 1.4 sig, 85mm 1.8 nik
35 or 50 most of the time, prefer the 50 for people shots since I don't have to get too close,
35 to get a little more environment. I would still prefer it a little wider if possible. (But the quality of this lens beats nikon's 17-35mm hands down)
85 is for the occasional tele, but even then its not sufficient.
Note that the Sigma prime lenses are generally heavier than nikon lenses. you will probably do just as well with Nikon's 35mm f2 and 50mm f/1.8g
If I have enough $, will wanna try 14mm 2.8 (rokinon), 35 or 50mm 1.4 an 135mm f2 to cover more of the extremes.
------All Zoom------
17-35 2.8 nik, 70-200 4 nik
Versatile, 17-35 for the environment, architecture, food, portrait, pretty much everything, 70-200 for events or areas that you can't get close to (parades festivities etc.)
I do find myself wishing for more bokeh, so a 50mm will fill in the focal length gap and bokeh gap nicely.
70-200 f4 is much lighter than the 2.8 btw.
(I have not tried using just the 24-70 alone, don't own it...)
----Just 1 lens------
Sigma 50mm f/1.4
You don't need me to tell you why a 50mm. All I can say is, I have not found a 50mm for nikon dslr that is super sharp wide open, focuses fast and accurately and renders beautiful bokeh, all in one lens. But nonetheless, a 50mm is the MOST versatile lens imo.
Sigma 35mm f/1.4
I found a fantastic lens for 35mm that is sharp, focus fast and has good bokeh, but it is a little too wide for street portrait, a little narrow for landscape (for my style at least)
Nikon 17-35mm
Its.... a love and hate. I love the UWA perspective at 17mm, and 35mm f/2.8 does allow some close and personal shots with decent bokeh. But I do end up cropping a lot of my shots just to get the perspective I want. And I do wish for something with better IQ (Just my experience. Defenders of nikon UWA, don't get mad at me).
Tips:
1.Weight is of utmost importance. Bring only what is necessary.
2.Know your style and bring what works for you. Think about what you want to shoot at the destination, or what you like to shoot.
Sadly, in my case, there are times when I want to be a paparazzi, times when I want a super wide perspective, and times when I just want a nice bokeh. so I end up bringing ~3 lenses for travel. I also dislike intruding pple's personal space, so I prefer something longer if I wanna take more street portraits.
3.AutoPanoGiga
Use this to your advantage. If you have only a 50mm like me but want to take a wide landscape, just stitch them up lo. It may take some time to process, but you will get a wide AND super high res photo
3.Flash, tripod, lightmodifier
I seldom use the tripod, though when I do, I am thankful i brought it. But not worth the weight. Same for lightmodifiers and flash. But if you must bring a portable set up, one double fold umbrella, one tripod (to double as a light stand) and an umbrella adapter is probably the lightest off camera set up you can carry arnd.
For something even lighter, I suggest a 60cm 5in1 reflector. Its so light, so useful for food photography, and in a hot country, it doubles a very powerful fan (I kid you not).
Cheers