More than one pair of long johns? I'm tall and skinny. A poor setup for delivering warm blood to toes. In my Boston and Ann Arbor days, I was known to use more than one layer of LJs.

Also (and this is big!) be sure you have full wind block on the fronts of your legs, especially thighs down over the knees. I used newspaper back in the pre-miracle fabric days over my thermals and under my riding tights or regular pants. Now I use wind front tights. I've also started using gaiters I made of windblock, semi-stretchy fabric and velcro over my ankles. I made them to shed Portland's rain on long rides but quickly found they were very nice in the dry cold. And I still sometimes cover my thigh fronts with plastic bag or newspaper to stretch the temperature range of what I have on hand.

For my long (and very long for my waist size) leg, I also make it a point to wear high socks that overlap fully with the thermals.

For me, the biggest thing is that I have to keep the warm blood I send down there warm. All of that blood is very close the surface around my knees. (I want to get them re-plumbed al-la bike hydraulics that run through the headset and bottom bracket but I am holding off until I can get those replacement ti knees with the proper hydraulic blood lines pre-installed. Perhaps not this lifetime but maybe I can spread the word and they will be around for the next.)