I'm not much of a gear junkie. Most of the stuff I take on a hunt has been in my pack for years, or newer versions of old items. As the saying goes, "If it ain't broke, don't fix it." That being said, there's also some stuff I've tried out that I've ended up loving after initially thinking I didn't need it or would hate it. Anyway, excluding the obvious (boots, arrows, rangefinder, etc.) these are the top 5 things I absolutely will not go hunting without. 

1.  Duckworth Polaris Henley - I can't say it enough, wear wool. One of the coolest parts about working with Schnee's over the years is seeing what new pieces Duckworth comes out with and having the ability to see, feel and test their new products. Their new Polaris fabric is the warmest fabric for its weight available. The waffle knit construction traps air and vents excess heat, and regulates temperature better than anything i've ever worn. I wear it as a base layer in all of my hunts. The henley version just helps dump heat even better when it's super warm. 
2.  Sitka Stormfront Gaiter - These were a new item for me last year. I always chalked gaiters up to being another unnecessary item that was more of a fad than actual gear. Per usual, I ate my words once I actually tried them. These specific ones from Sitka are super light, just plain old Goretex uppers with some Cordura on the inside for reinforcement if you're banging  your boots together or stepping over logs. They're pretty slick and just another thing you should probably throw on your gear list if you haven't already
3.  Black Diamond Distance Carbon Z Trekking Poles - Another new one for me. There's an episode of MeatEater where Rinella talks about how he always thought trekking poles were for softies until he actually tried them. I empathized with that. Now that I've tried them they're on every hunt. These specifically pack up super small and are crazy light. So if you don't need them, you'll barely notice you've got 'em. If you do get something down, I promise you'll be glad they're with you. 
4.  InReach Explorer+ - You don't have to get this exact one, just happens to be what I run. But some form of GPS/satellite messenger with an SOS button is just a smart thing to carry. It's rare something horrible happens, but if it does this thing can save your life. On top of that, if you've got friends standing by to come help you pack out a bull, or just want your loved ones you made it another day and are still alive, it's a great luxury to have. I use OnX for all my maps, breadcrumbs, and waypoints, but it's also nice to have a backup if/when my phone dies. 
5.  Trailshot Water Filter - If you're going to spend several days in the woods, some kind of water filtration system is a no-brainer. The Trailshot is just about idiot proof, packs up small, cost effective, and most importantly, works. One filter gets you about 2,000 liters, and they're easy to replace when you get there. My body is accustomed to being well hydrated, so I usually run out of water early in the day. When I do find water, I always break and bust this thing out.