I've been giving this topic a lot of thought lately as I have two unique (for me) trips planned for 2017, one short and one long. Both trips are essentially family trips, so it can't be all about daddy (me) shooting pictures all the time... I hope you don't mind if I share my thoughts about my own trips: maybe it'll help you to hear how other people think about these things.
I have a mix of primes and zooms and, like you, on a trip I want to maximize quality while carrying as little as possible. While I love shooting with primes, zooms tend to be what I build a trip around. Again, with kids in tow, I don't have as much leeway to "zoom with my feet."
I already completed the first trip for this year, nine days in Nicaragua. Great trip. For this it was one body, the XT2, and the 18-135, 23f/2 and 14f/2.8. The zoom was on the camera a lot, but I also used the 23, often wide-open, especially when shooting pictures of my family or wanting to look a little less consipicuous while on the streets (Nicaragua, however, felt very safe to me). The zoom was great because we were often on trails or in boats, with very little room to move. The 14 was used the least, but still worth carrying...I really appreciated going wide with it from time to time. While the zoom isn't as crispy as the primes, it was plenty sharp enough and there were many shots I got that I simply couldn't have gotten with a prime. It was well worth the carry. I will say, however, it was my third copy of the 18-135. I was not happy with the first two I tried. YMMV, but that is a lens that, in my experience, needs careful vetting before purchase.
The next trip I'm thinking a lot about for later this year is much grander: 7 weeks in Peru and Ecuador, including the Galapagos. This is more complicated, given the time and the varied stuff we'll be experiencing. Some of it will be about meeting people and the cultures (we're building a soccer field for a village in the Andes), some for learning (a couple weeks in Cusco learning Spanish with the family and visiting the sites, including, of course, Machu Pichu), and some opportunities to visit some beautiful places where landscape photography will all but demand some attention (Amazon rain forest and the Galapagos, to name a couple). Obviously, I'm very excited about this trip... But, wow, it's complicated to think about what to bring in terms of photo gear. I really want to keep it light and simple for such a long time, and deciding what to carry is difficult. I'm looking at these two options, and leaning strongly towards option A:
Option A, heavier, but with more reach:
XT2 and XPro 2
10-24
18-135
100-400 (and 1.4 teleconverter)
35 f/2 (or maybe the f/1.4) for portraits
Option B, lighter, less reach, less WR:
14 f/2.8
18-55 f/2.8-4
55-200
35 f/2 (it would be my only WR option in this case)
I'm pretty much decided on 4 lenses and two bodies either way. I can of course mix and match the above. I figure my XT2 will mostly host the mid-range zoom (18-135 or 18-55) and the XPro2 will mostly have the 35...then I'll swap in the longer and/or wider lenses as needed from time to time.
It really comes down to how much I want to carry that 100-400 for seven weeks of occasional use. I worry it'll be in my bag for weeks at a time, putting kinks in my back: but when I'll want it (the Galapagos and Amazon especially) I'll really be glad I had it. I think. All the other lens choices kind of come from that one decision in my mind.
I own other lenses, but I think 4 lenses, two bodies is the best compromise for me.
As to carrying it all and security, I've been looking at bags. For the amount of carrying I'll be doing, I decided on a backpack (I used a shoulder bag in Nicaragua, but will be doing a lot more all-day walking on the next trip). I looked at F-Stop, but decided on Peak Design's Everyday Backpack 30L. I also looked at PacSafe's Venture Safe X40 Plus with camera insert, for whole-hog security...similar to F-Stop's approach, but with a lot more security features. But, in the end, I really like the feel of the Everyday Backpack, and especially the ease of access to the gear... it's easier than most packs, and I'll be able to carry everything I need with it. It also seems to be secure enough for my needs.
Hope my rambling helps your thinking, even if only a little. It's fun stuff to think about.
Curt