This post will be a short one, it will cover what I like to use on my lower body for cold weather riding and racing.
First off lets start with covering the important stuff, Literally.
I use smartwool wool boxers that have a windblocker panel sewn across the front. Windproof Boxers like this are an essential item for helping to not freeze your Important parts off (The Ladies could benefit from windblocker wool undies also I’m guessing). While sitting on the bike, this position leaves the area between your legs very vulnerable to the winds cold blast.
Next layer added is a thin wool 260 weight Icebreaker or similar wool long john/base layer tights.
If the temps are in the extreme low range or my pace is going to be more of a chill cruising I tend to add a thicker wool tight like the 370 weight Ibex energy free winter tights on top of the 260 weight or some combination of those pieces depending on temperature.