Keeping warm can be a problem in winter fishing. There are a couple of principals of keeping warm that makes a big difference if you follow them.
1. The bodies main function is to keep the core warm. So in the cold the body sacrifices the hands, feet and limbs to keep your core warm. Even though your body was warm it may be you need some additional warmth to your torso so it doesn't reduce blood flow to your feet and hands. Primary blood vessels come close to the surface of the skin in the neck and wrists. If you keep these areas protected from the air, less heat will escape and will help prevent cold hands. So wear something to keep your neck warm. A Jacket with a hood does a good job of keeping the neck warm and stops heat from escaping. A neck warmer or Balaclava works very well. I have use silk, wool and fleece Balaclavas. I really liked the silk in moderate cold and the fleece felt nice next to the skin. Wool is the warmest but it aggravates my neck. The silk packed small and I could carry in a pocket until needed. Silk was warm enough for most fishing conditions. The trick is to keep the wind off of your neck area.
2. You can't beat Chemical Hot Packs for keeping the body warm. Put one in inside pockets over each side of your chest area. They get really hot (135 degrees) and last for several hours. You can also keep them in front pockets so you can put your hands inside to warm them. I would fish for a while until my hands were too cold. Stop fishing and stick your hands into the front pockets next the the Hot Packs and instant warm hands. Go back to fishing until the next warm up for your hands.
3. Fingerless gloves are very handy for fishing. Wool or Windstopper Fleece work very well. If you operate a boat and your hands are wet most of the time then Skin Divers Gloves (neoprene) work well. It is hard to fish with neoprene gloves. One trick is to wear a neoprene glove on one hand and a fingerless glove on the other hand. This combination makes it easier to tie knots and only one hand has to be in your pocket with a hand warmer.
4. Keeping my feet warm has always been the hardest. Especially as I have gotten older and my circulation is not as good. The best combination is wool socks with silk or poly liners. I prefer silk as they are slick and don't slide down inside of the outer wool sock. The warmest socks I have ever used were a wool and silk blend. Never put on the same socks two days in a row. They absorb moisture and you feet will get cold quicker than when you have on dry socks. The same can be said for your underwear. Wear fresh dry items next to your skin every day. The best foot warmer is electric socks. In really cold weather electric socks are hard to beat standing in water.
So the biggest secret to keeping warm is to keep good circulation to your feet and hands. Don't wear clothing or boots that are too tight. Tight clothing and boots will limit circulation and your feet and hands will get cold. The warmer your torso is the warmer your hands and feet will be.
Fleece, Wool or Silk Balaclava