Question: What’s the must have gear for “mountain photography”?

I guess the new 70-200mm GM lens should be high on my priority list for this

It’s New Year’s Eve. And for one time I will take the chance to ask you a presonal question. Next year I do plan to hike a lot on the Alps and I want to take the chance to take some great photos. I am absolutely no expert in “mountain photography” …or how should I call this? :)
I therefore wanted to ask the SAR folks if they can help me out by telling me what’s the best and must have gear. Here are some key info about my trips:

1) All trips are at High altitude (over 2.000 meter up to 4.000+)
2) These are many day long trips (means I will shoot in all kind of different light conditions)
3) I will also hike in harsh conditions (rain and snow)
4) I will hike a lot on glaciers
5) I will use the A7rII (or A7rIII or A9 if it comes out in time).
6) Obviously I can take only few lenses with me (although we are two people doing that and we can share the weight)

I need advice on which lenses to buy, filters, tripods, bags and book to get prepared for this. Thanks!

And I wish you all a great new 2017!