>>2063560For one good socks as others mentioned. Don't double up thick socks, you will both compress your foot (reducing blood flow and warmth) and compress the sock (reducing insulation effectiveness). Good merino wool. My goto is Darn Tough and yes absolutely warranty the socks when you wear them out. If you are out for very long rides, don't be afraid to stop and change into a pair of dry socks. When I am hiking I have 1 of everything typically except socks.
Air flowing past the body draws heat away. Additionally, your body is always giving off heat and a lot more when you are pedaling. By providing a wind layer you will trap your body's heat. The easiest is something to pull over the shoes and ideally over the ankle as well. In a perfect world, it's something fancy like goretex or similar 3-4 layer fabric. Those fabrics are semi permeable and will allow the heat from you body to push moisture out through the fabric without letting water or wind in. For your feet though it's not the biggest concern to spring for that and if you are really cold an impermeable barrier might be best, like an neoprene over sock. Your sweat will be trapped but it will certainly keep the heat trapped too.
Don't neglect the torso. If your core is cold, your body will contract muscles and keep warm blood close to the organs. Keep your core warm, keep your limbs warm.
Hydrate. As someone who has poor hand circulation I have found that drinking plenty of water increases blood volume, which in turn improves circulation in the extremities.
