Taking chairs? Sit on something insulated, like a CCF sleeping pad. Sleeping pad is longer than a sit pad, helps prevent cold back and butt while the fire warms your front. Fill up a Nalgene with hot water, stuff it inside your jacket (depending on how lightweight your jacket materials are you may want to wrap it in something so the hot plastic bottle won't melt your thin jacket lining). Try fleece boot liners for extra warmth; up your game with down booties. Eat: get your metabolism going. Pee: don't ask your body to keep your internal tank warm, empty it out. Disposable hand warmers can be "saved" for later: bring an extra plastic zip top bag, when you're done using the warmers suck out the air and seal it up to stop the iron bits being exposed to oxygen, thereby temporarily stopping the reaction.