Lights.Get some, when you have got some get a few more, when one is flat or un-charged you have a back up. I have them for sale in both workshops for £5. If you are looking for more durable quality, I rate Leyzne they are not the cheapest, but they are good.
TiresRiding round with your super skinny summer tires on is probably a mistake. Get something with pattern on it and and think about sizes 28mm and above. You need rubber on the ground so consider running your tires at lower pressures whilst it is wet and icy. Go for 70-90psi rather than 90-110psi on road and hybrid bikes.
Wash your bikeNobody likes doing this especially when its dark and cold, but washing your bike once a week will reduce wear and keep it running better through the winter. There is a lot of salt on the roads currently, this eats bikes. Come and wash your bike in the workshops, it is warmer and while you are here help yourself to chain lube and silicon spray. If you are doing it at home a bucket of hot soapy water and a toilet brush works very well. Just make sure you oil the chain and gears when you have finished. NEVER use a pressure washer it will wash all the grease out of your bearings. This is a bad thing.
Watch out for Black IceEasy said, it's hard to see because it is see-though. However if it has been wet and then frozen overnight be super-aware. Be equally careful on adverse camber bends when it is freezing. Do not as I have done too often, think that you can ride on ice, you are wrong. If in doubt get off and walk. I am straightening quite a few dropped bikes this week, so far no riders have been badly bent.
"There is no such thing as bad weather only bad clothing choices." You are grownups, enough said.
Happy Christmas and a viable New Year.