Let's see: layers, layers, layers!
thick, wool-blend socks.
A brown, cotton t-shirt left over from the old Army days.
Army cold-weather system insulated underwear (the brown polypropylene stuff).
A wool-blend, brown Army 5-button placket sweater.
9-oz. Chamois pants.
9-oz. Chamois shirt.
1,000-grain Thinsulate boots when the temp drops into the 30's. Somehow, when I'm 30 feet up in my stand, and air can circulate beneath my feet, it always seems colder than it actually is after sitting for a couple hours.
I've got a little felt-like wrap that velcros behind my head which covers my chin, nose and cheeks which I put on when it's real cold, and then a fleece hood/baclava thingy pulls over that.
That's about it. Actually, it doesn't sound like too many layers once I put it in print, but that right there keeps me warm even when the temp drops into the teens. Once it's in the single digits, I'd have to pull out a coat/parka and probably have to put a pair of sweatpants on over the underwear and under the chamois pants, and make sure I had my "hot hands" with me I could break open throughout the day.