Wear a pair of boots that won't make your feet sweat while walking in.
Then put these (
Cabela's -- Icebreaker Insulated Boot BlanketŪ Overboots) on and your feet will stay warm.
I had a TERRIBLE time keeping my feet warm until I went to the boot blankets.
The other thing I do now is also carry an extra pair of socks in with me in case my feet do sweat. I will dry my feet and put on the other pair of socks so my feet are not wet.