Today's quick tip: If you have problems keeping your feet and hands warm while cycling in the cold, wear a hat!
When your core body temperature starts to drop, your body autonomically directs blood flow away from the extremities and into your core. Keep the core warm, and you retain blood flow to the extremities.
You lose most of your body heat through your head, and a hat is an easy way to regulate your comfort.
You should still wear protective gear appropriate for your weather conditions and riding distance, but putting a hat on goes a long ways to improving your comfort when cycling in the cold.