I'm just planning on wearing a long armed T-shirt, probably with a thin rugby shirt type thing, and a thin fleece, slightly warmer than my normal commuting wear. I'll carry a spare fleece top, and my Goretex for rain. I'll probably just wear mitts. People hate me when it's cold, I just seem to run naturally hot.
Having said that, I'll also carry an emergency backup pair of gloves, overshoes, ear warmer thing, and cap.