My vote was for the Nokton 50, Rokkor 28 and Hologon 18. The Nokton will cover any low light situation, the 28 will do general shooting, and the Hologon will let you capture everything that your eye sees, if that makes sense. It would be fantastic for being indoors at a cathedral, for example.
My travel kit for my M9 has historically been:
Zeiss Biogon 21mm f2.8
Voigtlander Nokton 35mm f1.4 MC
Leica Summicron M 50mm f2
In 2010, I went to Japan with this kit, along with the Voigtlander Heliar 75mm f2.5, Ricoh GRD III and Canon S90. The S90 was hardly used, only to take videos. I wish I had taken more videos! The Heliar 75 didn't get much use, so my travel kit from then on was just 21, 35 and 50. This focal length range gives me everything I want, from capturing wide expanses and indoor scenes to low light portraits and street shooting.
For a 2013 trip to Hong Kong, I took the same kit of M9 + 21, 35 and 50; and I also took the Olympus E-M5 with:
Panasonic 14mm f2.5
Panasonic 12-35mm f2,8
Olympus 45mm f1.8
Olympus 75mm f1.8
The Ricoh GRD III also came, taking many snapshots. But the bulk of the work was captured with the M9 + 21 and 35, and E-M5 with 14mm and 12-35. The 45 and 75 saw a bit of use during a birthday dinner and through car windows, but not much else. The Olympus was a huge boon for video, allowing me to shoot ages and ages of it at any time.
On another trip in 2017, I took the same M9 kit but the Zeiss Sonnar 50 instead of the Summicron, and changed the E-M5 lens setup to:
Olympus 17mm f1.8
Olympus 25mm f1.8
Olympus 45mm f1.8
Most Olympus images were shot with the 17, giving a 35mm focal length equivalent. As the E-M5 is so small, it was almost like a pocket camera, especially with the 17mm. I also carried the Panasonic LX7, which was excellent for wide angle snapshots.
My preference for travel photography is to have a lens that is wide enough to capture what my eyes see, which means entire rooms and surrounding context of subjects. 21 suits me perfectly for that. A fast 35 handles night shooting and environmental portraits, and a fast 50 is like a portrait lens in comparison.
Now that I have the Distagon 35, the new travel kit will be:
M9 + Biogon 21, Distagon 35, Summicron 50
Panasonic G9 or GX85
Sony RX0 for pocket camera
The lens kit for the m43 camera will depend on which camera I take. The G9 being larger means it will balance with larger lenses, so I could easily use the 17 and 25mm f1.2 Pro lenses, and the tiny Olympus 12mm f2 for general shooting. If I take the GX85, I'll use the small Olympus primes instead. The GX85 has excellent video quality, almost as good as the G9 at 4k.
At this stage, I'm unsure how the Panasonic S5 fits into my travel kit, as the lenses are larger than I like unless I use adapted M mount or Minolta Rokkors. I don't have a set of Panasonic f1.8 or Sigma f2 primes yet, so we shall see how that goes.