I live in a place where in the middle of summer, it can snow. So I have always toured with an additional layer of clothing in my panniers, just in case. It has served me well over the years.

Two of the better acquisitions for me have been light fleece jackets from Decathlon in France, under the Quechua brand. They are full-length zip, but of a very light fleece, so they compact down to a small pack size, and they are warm to wear over my other tops and under a waterproof jacket. I like them also for their wicking capability to keep whatever tops underneath as close to dry as they can be.

I mention them, because I have yet to find in Australia and Canada tops that are of the same light fleece material.

Light thermal tights, a thermal top, and a light toque (we call them beanies in Australia) plus some long-fingered gloves would be a minimum requirement for me. Plus waterproof pants and top, generally to keep cold wind out.