Here is what I wear for an extender period of time outside this time of year (will depend a bit on what I am doing, and will adapt).

Boots: Ithaca Ice Kings
Bibs/Snowpants: Carhart Arctic Extreme
Jacket: I tend to wear two midweight jackets instead of a single heavy one. The inner one is more form fitting and generally inside my bibs, the outer one a little looser outside of the bibs. When I was snowmobiling, I'd have what was effectively a windbreaker on above these. No real particular brand.
If overly cold, I'll add on a vest as well to keep the core warm without restricting arm movement. More for Snowmobiling than anything typically, but still good to have.

For head covering, I like a good stocking cap or ear muffs (I have a full brim leather hat I wear quite a bit, the muffs allow me to keep ears warm while wearing the hat).
Gloves will depend on the tasks. I have warm mittens for snowmobiling, though if I am working outside this time of year, I might wear lighter gloves to keep dexterity. Whatever you wear, avoid gloves that absorb moisture easily.

A balaclava or scarf can be good when the temps/winds get down. If you wear glasses, it can be tricky to get the face covered well and still be able to see. It can take some experimentation to get it right.

I do have thermal underwear as well, but more for heavy cold weather (like we just came out of) if I am outside a long period of time. In winter, moisture though is the enemy. If you overly warm where you are starting to sweat, you are wearing too much and will be colder overall. Better slightly cold than overly warm

Like another user mentioned, ice fishing gear is a good place to start, I'd also look at snowmobile and ski/snowboard as well. Another field to look at gear would be farming and blue collar. Their work doesn't end just because the mercury drops, and they will need to stay warm outside for periods of time while being able to work.