I finally have this cold weather thing figured out. It took ages, but now I can do fieldwork in both absolute cold (well below freezing) and wet cold (deep snow, temperature just below freezing, pouring rain) all day without misery or risking hypothermia. The factors that keep me warm, from easy to adjust to... not:
1. Breakfast is critical. I cannot have too many complex carb/protein/fat calories the morning of a long day of fieldwork in the cold. I need to get all that energy in early because...
2. If I eat anything more than a snack during the day, my body works on digestion instead of keeping me warm, and my core temperature crashes. This is backwards and strange, but I am the sort of person who will start shivering after a big meal.
3. I'm better off staying out in the cold, rather than warming up. If I get toasty at any point, my system goes, "oh good, we don't need to worry about dealing with cold any more" and then I'm miserable the rest of the day.
4. Keep active. Sometimes I'm just watching other people do work, and if I just sit there, my circulation goes down and then I have a serious extremity problem. I have no shame doing "the cold dance" - bouncing up and down on the balls of my feet in place (so I'm not in danger of slipping) if my feet start to get cold.
Many of my "gear" posts are about the stuff I wear. It took a lot of experimenting to figure out what keeps me warm, but not overheated, in all sorts of conditions. How many layers are too many? Is there a possibility of getting wet? Will I be fighting through brambles? Maybe the knits and high-tech outer layers need to be replaced with something sturdier. How can I fit the PPE (personal protective equipment) I'm required to wear in with the cold-weather gear?
I almost called this "grit", but that's not quite accurate. What I mean is, I've had lots of practice being cold. I shiver and turn funny colors easily, but there's a difference between "brrr!" and dangerous. I've learned to adapt to the cold, and I can stay comfortable (or uncomfortable but safe) for longer and at much lower temperatures than when I first started out.
I matured super late, physically, and was still in "colts years" into my early 20s. I've gained 30 pounds on a small frame (and remember, I'm a short woman!) since I started working in the environmental biz. Where did that weight go? Big muscles in my shoulders, upper arms, and back, from hauling coolers and other equipment. Same thing with my legs and butt, from hiking around all day with said equipment. My hips and boobs, from general weight gain and finally developing a "womanly figure" after spending what felt like an eternity (middle school, high school, early college) with no assets in that department. And yeah, I do have a pooh belly. That extra mass - everywhere - really does help.
I wouldn't say that I enjoy spending the day outside when it's miserable out. But I can do it for weeks on end without any ill effects, and then I have a bounty of war stories to impress newbies/scare my parents/negotiate for raises in the future.