I haven't been doing this lately, but I think I'll start again. I often get out in the cold and discover I'm dressed a little lightly. Especially if there's a strong headwind. I do pay attention to wind chill forecasts, but it is occasionally hard to dial in just right with clothing.

Solution: carry an extra pannier with one extra layer for riding. As well, carry a heavier fleece jacket and extra mittens, cap just in case of a breakdown or a passing car nails you with water. The additional weight is less than 2 pounds and worth it as an insurance.