Looks like you've gotten enough recommendations on clothes, so here I go...

After you've figured out what to wear, which is always a compromise between movement/heat factor, bring along some empty carbs. I like M&M's. They don't stink too bad with the candy coating and they taste great. Eating a few handfuls is like throwing a log on the fire. Next, if I'm still cold, I put my poncho over my clothes, and it works pretty well too. Or just be tough!

just kidding!