Anyone who's spent time in the outdoors during cold months knows that layering is the name of the game. Warm comes from trapping warm air next to the body, and insulating that warm body heat from the cold outside air. This is done with a bottom to top system of layers that work together to keep you comfortable and alive.
The first layer is known as a base or under layer. The main job of the base layer is to wisk perspiration from the skin and creates the first level of warmth. I personally use NRS WaveLite XT tops and bottoms, and IceBreakers 200Lite series tops and bottoms. The NRS WaveLite XT is a medium weight set of nylon/spandex blend fleece, while the IceBreakers are a lightweight wool base. Pick out what is appropriate for the weather and water you are going to face. The lighter weight of the IceBreakers makes them very useful during much of the year from Spring to Fall, while I break out the heavier WaveLites for the winter months. Since I paddle my kayak (and not pedal) the NRS bottoms also make fairly regular use through the year. A performance sockliner is also recommended, and I again like my IceBreakers. This lightweight base wicks moisture away from your feet. A dry foot, like the rest of your body, is a happy foot. Whatever you choose, it’s important that base layers are made of moisture wicking materials like polyester, microfiber fleece, and wool. The heavier the weight, the more warmth it holds.
Mid layers continue the insulation started with the base layer. These layers should continue to be moisture wicking, but more importantly, capable of trapping air to create warmth. Ideal materials for the midlayers are manufactured from Polyethylene (PETE) fleece and wool. These should be looser fitting than the base layer, which is normally skin tight. I have a variety of polyethylene fleece that I use for mid layering from lightweight jogging wear, to some super-heavy duty PETE fleece I found at Cabellas. For the most part, no namebrand stuff in my midlayer. All I pay attention to is the material. For maximum warm, it’s sometimes best to wear a few lighter layers than a single heavy layer. Generally, my coldest days (22*F) has included both a lightweight and the heavyweight fleece. Warmer days you might not even need a serious mid layer. Again, let’s not forget the feet! A good pair of SmartWool socks over the liners should keep them nice and toasty. Also consider some waterproof socks like Seal Skinz or NRS Expeditions.
In the end, I think the shell or outer layer to be the most important of all the layers. Should, for some reason, you find yourself in the water your mid and base layers could quickly be useless if they get completely wet. This is where drysuits come into play. By finally sealing of the water, and the wind, you're going to be comfortable, and alive. Naturally there are a couple schools of thought when it comes to dry suits and water protection. Use what works for you, and for what your think your life is worth. Breathable fishing waders and a dry top make for a great combo, but nothing is as waterproof as a dry suit. Palm, OS Systems, Kokatat and others make great dry suits with relief zippers, and rubber or neoprene cuffs to keep the wet out. Personally I pair Kokatat Temptest drypants (they have a built in waterproof sock) and a dry top. The two interlock better than the wader/drytop combination. I can tell you though, when the budget can afford it, you can bet you'll find me in a full dry suit. It is important that the outer layer is breathable to help wisk away the sweat all the inner layers have pulled away from your body.
Footwear is one of the things most guys I know ask about. Being the furthest appendage from our heart, they're the first to get cold. A waterproof outer helps me out a lot. With the sock liner and wool socks, I've been OK. Most kayak footwear is neoprene, and since you're body heat can't get to it, the neoprene gets cold. In the winter I actually wear sandals. They don't absorb water so they dry quickly. When choosing footwear, it's important not to get too constrictive. You'll often need shoes that are a couple sizes larger than you would normally wear. Too tight and you'll reduce that warm blood flow to the feet.
I almost forgot all out gloves. I personally don't use them but in the most extreme situations (never used them snowboarding either - nor with my aluminum paddle at below freezing temps), but gloves are another hot topic amongst kayak anglers willing to brave the winter months. There's one glove manufacturer most guys here in the PacNW swear by - Glacier Outdoors. Glacier Outdoors makes gloves for a variety of different purposes - fishing and kayaking being two of them (but not a kayak-fishing glove). The Pro-Angler gloves offer fleece lined neoprene gloves with slitted forefinger and thumbs, so you can easily tie knots without removing the gloves. They're also pre-bent making fishing and paddling more comfortable.
Glacier Outdoors also has a couple neoprene beanies to help keep your head warm too. I've been debating adding one of these to my winter fishing gear, but so far a SmartWool liner under a REI fleece beanie has been good enough.h.
Hopefully this has set you off in the right direction to keep yourself protected this winter. Get out there and enjoy winter fishing. Just because there are a few snow flakes, doesn't mean you shouldn't be fishing.