Surely of all the manifestations of the Trad/Americana/Whatever style 'Downeast Duck Hunter' is the warmest.
The basic rule of this style is that everything you wear can be greatly improved by lining it with flannel. The more flannel the better.
Layering is also important. In fact the ideal silhouette for the wearer of the D.D.H. look is nicely bulbous like a hand grenade as you pile on layer after layer.
LL Bean and Woolrich are the style leaders I think, with Filson a good runner-up. Pendleton is for the Gentleman Duck Hunter.
Other countries and cultures pursue their fowl in Tweed jackets and Tattersall shirts. This seems like Dandy Duck Hunting to me and lacks the rugged charm of the Downeast style. Also it's damn cold.
Some also Duck Hunt in bright Orange (to stand out) or camouflage (to blend in). I suspect that these are the people who actually want to shoot ducks and aren't concerned with style at all. We shall ignore them.

Let's unpeel our idealised Duck Hunter rather like an onion from the outside in:

'Canada Goose' Halifax Parka. The best looking Parka. Also keeps you warm in -40C, but that is incidental.
Field Coat. Useful for pockets. Button in a liner for another layer if needed.
Ragg Wool Sweater. Get the heavy button-neck kind.
Flannel lined Canvas shirt or (better still) LL Bean Chamois Cloth shirt. Plaid or plain.
Dark Green Polo shirt. Collar flipping is allowed to stop your scarf from chaffing your neck if it is not made of Cashmere.
Plain White T-shirt.
(You could also wear long Silk underwear but that seems a little too practical to me.)
Flannel lined Khakis with BIG turn-ups to show off that they are flannel lined.
Red Tartan Flannel boxer shorts (for a little touch of Christmas cheer).
Huge thick Ragg Wool socks with ordinary cotton crew socks worn underneath.
Bean Boots/Redwings/Timberlands.
'Mid West' Deerskin Thinsulate lined Work Gloves.
Large Hip flask.

Wearing this weight of clothing makes carrying a gun impossible, which is just as well as the above look is best worn in the city and not out in the dirty, muddy, smelly countryside.

T.L.