My first choice would be quality boots. I've worn old school Vasque Sundowners for decades and will continue to wear them. Each pair lasts about 10 years and my feet never complain.
If boots are out it would be a quality merino zip-up. I use a First Lite Labador on every hunt almost regardless of weather. It's my top layer when I'm walking around in the fall and it's a mid layer when it's cold in the winter. When it's warm and I only want to bring 1 warm top layer, it's my Labador...
A waffle fleece layer. I have 2, Patagonia r1 with a hood, and a marine surplus 3/4 zip pullover. R1 is more technical fabric, but I love that surplus fleece. Cheap too, 30 dollars.
Merino base layer. Since that is two pieces I'll pick the one that never comes off. The Chama hoodie. I wore one for 10 days straight all day and all night last September. I had used it numerous times before and loved it, but it really proved itself on that trip. I think I can get another season or two out of the one I have so I haven't tried the newer Kiln hoodie. The Chama improved.
I second the First Lite Chama Hoodie. I have a bunch of them. My favorite is the ASAT camouflage. I wear one on every hunt. Even when it is warm I am comfortable and it helps keep the bugs off my head when I need to sit still. Never tried the kiln either because I have to wear all these Chamas out first.
Sitka Jetstream jacket water resistant and great all year round for any time of year. I run this in summer scouting for the morning cold and us it pheasant hunting in December.
If there's absolutely one piece of gear that goes with me on all my hunts and even just cooler weather, day training hikes, it's a warm, windproof beanie. I usually carry an OR but if I expect cooler temps. than I carry a Sitka Blizzard beanie.
Boy I went for an atv ride to my hike in spot, didn’t want to wear my attacks on the wheeler for 20 miles. I wore my old insulated hunting pants. Horrible! Nothing felt good, I was so excited to get them things off and into my attacks!