The obvious would be long cycling pants. Whether you want to go with lycra skin hugging type such as typical shorts or a looser fit is probably preference and weather related.

Vest made out of Polar Tec. It is light weight and warm. Full gloves. If you don't need sunshades get some clear goggles so you eyes won't water in the cold.

Turtle neck shirt to go under the vest.

Full gloves.

Helmet: I've got a summer one and winter one. The winter one has less vent holes. Also, there are these ear warmers that fit over the ear. Not like ear muffs that are connected. I think the last place I saw some were Eddie Bauer or LL Bean. They are oval shaped, made out of something like Polar Tec.

If it is wet and sloshy you might want to consider fenders to keep water and mud from being slung up on your back and neck. Which brings to mind a rain poncho.

If it is extremely cold and you need a gaiter or full face mask toboggan I'd suggest hot cocoa laced with Buterscotch Schnapp's, a down lap blanket, a cat curled up in your lap, and a good book or movie!

Disclaimer: I'm in west Texas so I can only go by what I am planning on wearing.

Oh! One more thing. Get some good lube for your chain and apply it religiously. I use Pedro's Ice Wax but Pedro's Synlube MTB is for extreme cold.