The most important lift should be lift yourself out of the computer chair logging off of here and getting to the gym/outside.
I really can't take anything they say seriously after seeing the deadlift picture. They then say to get some coaching first. Were they talking to the guy in the pic???? Then they make light of squats as we don't squat dead animals. Yet include the Turkish Get Up as if we may be inclined to try that in the mountains for some reason. Bad article.
I would say
Squats
Deadlift
Situps of any kind: not a lift but core strength is paramount in balancing and maintaining stability with a loaded pack
Here's my real question...why are we limiting ourselves to just 3 lifts? I train usually 5-6 days a week and each day is a different lift, which usually consists of squats (and it's variations), deadlifts, shoulder press, bench, cleans, ect. I also try to do some kind of cardio 5-6 days a week (which means I usually do two-a-days). Cardio is a mix of slow/steady, sprints, and pack work. So, with all the options, why just pick 3?