Wool, lots and lots of wool. Or from what I read but haven't tried out alpaca is even better. Alpaca sweaters and socks can be found at decent prices, lower prices than wool a lot of the time.
Fashion isn't on the list of priorities at all, most of my wool sweaters I picked up for under $10 at thrift shops or second hand stores. Of course a layer of long underwear shirt and pants underneath then I put on an undersized wool sweater, one with short sleeves but not tight, then a larger sweater over that. A high neck or turtle neck sweater is nice but wool rubbing on your neck all day or night can be slightly uncomfortable, a turtle neck alpaca sweater would be great for this, alpaca doesnt irritate like wool. Or a turtle neck undershirt to keep the wool from rubbing against your skin.
Outer wear can be done two ways, sometimes I wear a carhart jacket and sometimes a thin wind blocking gortex US Army surplus pants and jacket, they both work, gortex can be noisy in the cold but it does work great for the wind and with layers of wool underneath you stay nice and warm.
Wool pants can be a lot harder to find, search for old army surplus stuff, something like this
Wool pants Then gortex over that
Army surplus gor tex suit That's an unbeatable price, they are triple layer gortex, for the equivalent from some name brand the jacket alone would be around $300.
When it comes to boots and gloves you want large and loose so you can fit, of course, more wool. The more your feet move around in the boots the more friction and more heat. It doesnt matter if you buy 2000g thinsulate boots, if they're tight they will keep you less warm than 400g thinsulate loose boots.
Last month I got a screaming good deal on these mittens
Outdoor Research Firebrand they are the warmest mittens I have owned. I got lucky and got a new pair for $50 but they were sold out the next day, from the manufacturer they are $320 but you can find them cheaper searching around, again get them large and wear a small pair of gloves underneath so you can pull them out to shoot or mess around with small things.
Last and maybe least I like a pair of gaitors for my legs, they help a surprising amount keeping your feet warm without having to get bulky boots and they ether keep my gor tex pant legs from rubbing together and making noise or they protect the bottom of my nice wool pants from thorns and twigs tearing them up.
A neoprene face mask is great also, especially in the wind, even a clear tight fitting pair of safety glasses is nice for the wind, -20 or more windchill and snow or ice blowing against your eyeballs isnt nice. And not a brilliant choice but head wear is where I slack the most, I just wear a cheap stocking cap over a ball cap, the hood on the gortex jacket helps, any hood really helps. Mad Bomber type hats are great for warmth, usually too warm for me, Mad Bomber can go to [beeep] because they're made in china from farmed rabbits but do a search for a nice fur trapper hat, you can spend as little or as much as you want there, from faux fur to beaver fur and everything else in between.
Almost forgot, for when you are hunting a seat is a must have, sitting directly on the snow sucks, your pants end up melting snow and getting wet then when you get up again they freeze solid then you ether have a wet butt or an ice butt for the rest of the trip, find a small foam pad to sit on. I use a cheap turkey hunting vest that has a seat as part of it.