Optics are, in my opinion, the 2nd most important gear you have, the 1st being your weapon. I currently use Vortex because Quality and warranty are as good as anything else.
A good pack that can carry weigh comfortably is critical in the field. It helps you physically and mentally perform at your best. If you have a pack that doesn't fit correctly it can cause multiple issue but most importantly less time in the field.
I choose to use a lot of Stone Glacier gear because their gear is designed for one purpose backpack hunting and I have yet to have a failure with anything Stone Glacier.
When you're in the field, what's going on inside your body is just as important as what's going on outside. I love supplements from MTNOPS and Wilderness Athlete.
Clothing is very important in the field and having the proper clothing can mean the difference of leaving hunting due to weather conditions.