Newspaper! It was 3 degrees F this morning and my feet were fine. My commuter bike has loose toe clips/cages and I wore wool socks plus a sheet of newspaper wrapped around the front of my foot. Then I put my sneakers on over. It is amazing how well this works. As it gets colder I usually make myself a nice newspaper "footie" with tape that won't fall apart.

Neoprene booties and other items just make my feet sweat - this is the only thing that works, and it really works well!