New to winter riding - what clothes I must have?

[Owlie]

Long-fingered gloves, preferably that fit loosely enough that you can get a liner glove in there if you so choose.

Layers. Everyone is a little different when it comes to how warm they want to be, but layering gives you some flex as to how much you put on and take off. My wool baselayers have been the most consistently-used things in my winter riding wardrobe. (Before you give me quizzical looks, I moved to AZ from Ohio, and would ride in winter provided it was above freezing and not too windy.) I liked layering a wool base layer, and a long-sleeve jersey under a jacket (fleece-lined with an outer shell). I also have a windbreaker-type jacket. Arm warmers are also nice--instant sleeves, and not terribly expensive. (Sometimes I'll layer arm warmers under a long-sleeve jersey.) Shoe or toe covers are also cheap. Wool socks.

You don't necessarily need cycling-specific stuff. Check thrift stores for lightweight (all wool!) sweaters, just make sure they're soft enough that you'd want to wear them next to your skin. My preferred tights are running tights. (I actually prefer running tights because of the lack of chamois, so I can wear whatever shorts I want with them.)

Oh, and a wicking sports bra if you don't have one already. I cannot tell you how much better that made my life once I switched from cotton.