Don't just throw away those little disposable winter hand warmer packets after you've come in from the cold. Most of them stay warm for hours, and you can use them for many things! Toss them in your bed to warm it up before you go to sleep. Set your mug of tea down on one to keep it from getting cold. Hold some against whatever muscle of yours is achiest from exercise. They're really like tiny heating pads!
I will confess I have some tucked in my bra right now, after a very cold walk home from the gym.