A bag,whether it is a frame, handlebar, saddle or any other type, for me, is a necessity. Layering is key and being able to take off a layer when necessary, and have somewhere convenient to stash it, is important. Do not wait until you are already sweaty to take off a layer. Once you get chilled with damp clothes, staying warm is, at best, difficult. Also be ready and willing to just stop and take a short break. Keep your system fueled up. Riding a bicycle really amps up the wind chill factor. I like a wind barrier type, thin outer layer. The area above the chest has a large heat loss factor. It takes some experimenting and time to figure out what works best for you.