I'd say the most important piece of equipment is " YOU".
If you are not mentally and physically able and prepared to do the hunt, you will most likely fail. Show up in Idaho out of shape and hit the Mountains hard for a few days and you body will tell your mind, to hunt near the truck or just road hunt for a few days. Your mind will start making excuses, "too hot" , "too Many Hunters" "too many fires" , "tough winter last year" , etc. Our minds are full of excuses.
I work out all year long so when the season comes, I know I can get up to 9,000 or 10,000 feet and spend the day chasing critters and do it day after day.
I make sure all my gear is good and in proper working order so it won't fail.
Great question and so many good gear ideas and responses. 2nd Clothes / boots 3rd, Weapon, 4th Shelter / Bag / Sustenance .