4-6 wgt fly rod and floating line.

Floating fly lines will satisfy most of your fishing needs. A sink tip or intermediate line is good for searching but not essential.

Reliable tippet material - this is essential. I have seen a lot of trips ruined thru the use of “Hi-Tech”, “latest & greatest” or the “most expensive” tippet material. Most don’t tie good knots. There is no need to fish ultra light either. If you must bring high tech stuff along, make sure you have some Maxima you can fall back on when the other fails.
I extend this warning to hooks as well. Some of the fine chemically sharpened hooks will straighten (or snap) on hooking a fish.

Polaroid sunglasses are absolutely essential. Make sure they are not scratched. Optically correct glasses are less likely to cause headaches.

Hat. There are 2 types of hats, good and bad. Good hats stay on your head in all fishing conditions, bad hats continually blow off. Bring a good hat. It must also have enough brim to shade your glasses (and face) and it should keep your head warm. An Akubra style hat with toggle and a polyprop balaclava are an excellent combination.

Gloves. I rate these as essential if you are not used to alpine conditions. It can be very cold at first light (and right through the day). Numb fingers will spoil the experience.

Vest. These items should all be in a vest. It ideally should accommodate a waterproof jacket and lunch etc.