When I really stop and think about what a true “game changer” is, IMO it is something that directly contributes to putting more deer on the ground. I mean that is the “game” isn’t it. Oh yeah, I know…it’s the “experience, getting out, etc., etc., but let‘s face it, if you weren’t out to put game on the ground would you still be out strolling around the woods just for the “experience, getting out, etc,.? Prolly not. Most stuff falls under the categories of nice to have, makes me more comfortable, makes it more enjoyable, etc., vice actually helps me kill more deer.
With that in mind my vote goes on three things: GPS or similar nav aides that opens up new areas and new opportunities for most folks. The excellent choice of clothing available today. Can’t kill them if you won’t go because it’s cold out and you know you will freeze to death. And lastly, gear that promotes mobility. Got pushed out of my trusty permanent stands once upon a time and ended up on a 5 gallon bucket. I killed more deer off that bucket then I ever killed out of those “trusty” stands. Being able to stay mobile and still get up a tree is a little slice of heaven.