I commute year round on my bicycle and have done so for years.

Generally once the weather goes below 0°C I start with the toque and start wearing long underwear beneath my jeans. Throw a windbreaker over a sweater like jacket. I will throw some wool gloves over my regular cool weather riding gloves as well.

Once the weather gets in the range of -5°C or colder the balaclava comes out and thicker winter gloves. Wear a proper winter jacket and water proof slip on pants over the jeans. Also keep a pair of snowboarding goggles in my bag in case of very snowy weather. Would also recommend waterproof footwear of somekind when snow and slush begin to show up.

Definetly trying to scrape some ideas from reading this thread myself. I don't want to bring a pair of waterproof foot wear if I can help it. So I'm reading through here to see if I can spot anything useful for that effort. The fogging goggles is another thing that could be improved on for those particularly nasty snow days.