For hats, ditch the normal bushcrafter wide brimmed hat in the winter. I do as I find the blasting wind rips it off my noggin anyway, and it does keep your head warm, but not as warm as a Lowe Alpine Mountain Cap. I've had reason to take the hat off in the past as my head felt it was on fire! Best 15 quid I ever spent was getting one of those hats. Mot the most stylish thing, granted, but it's not a fashion parade in the woods. A shemagh is another great bit of kit, use it as a loose hat at night, a scarf during the day and as a dish cloth for drying up. They dry OK in a breeze too.
Wear wool, its' benefits far outweigh the downside, bulk and weight. Light weight shirts made from wool can be had on eBay, search for Pendletons and variations in spelling. Also, try the Shirts KF, old woolen military shirts. They can be a bit itchy, an old trick was to shave the inside and iron them inside out. Personally, I'd wear a tee underneath. Yoiu won't need to with the Pendletons shirts, they are quality soft wool.
Try a Swanndri type shirt for a second layer. Bison also do a shirt which may suit your needs, it is thicker and denser weave as far as various reports tell. A windproof shell would be needed over the top to stop the wind striping your heat away. Ventile or gaberdine, dense cotton canvas type jackets and goretex type shells should be considered. If you don't want to go synthetic, you'll need some sort of waterproof, a poncho in either rubber, nylon or ventile if you have the cash!
The legs are quite big but seem to be overlooked somewhat. It's like we pay so much attention equipping our hands, feet, head and torso but just let our legs look after themselves! A good set of solid trews with a pair of tights underneath will really do wonders. Tights used to be used in the forces before thermal garments were issued. They really do work, but make sure you don't get too drunk and strip, you'll never live it down! Gaiters can help keep your legs warm, not only protecting you from water and thorns, they will trap a layer of air again and insulate your legs and protect them from that chilling cold.
All this kit is for wearing during the day, as soon as it is gonk bag time, you need to rethink things. No point getting into your gonk sack with damp or wet gear on. People put wet kit in their bag to dry it out at night. Do not do this! It is extremely foolish. Your bag will get damp, and you will get colder each night as your wet kit transfers it's water into your gonk bag. Treat your bag with the utmost care, it above all things should remain bone dry. If the day looks to be fine, air it out as best as you can. If it is damp, there's not much point in trying!
Massive post, sorry about that, but I hope it is useful to at least a few people. remeber, lots of layers during the day, keep your gonk sack dry at all times, and the comment about going for a pee is spot on. Have you ever noticed that when you do put it off and go in the morning, the steam is like somebody let off a smoke grenade? That's the heat that your urine has sapped from your body core, you've wasted energy heating up your pee. Get up and go as soon as you need to.