Thinking of turning your winter jaunt into an overnight? Could be a lot of fun, if you know how to stay warm. Use the following tips as your guide to nocturnal heat generation and retention:

• Fluff your sleeping bag before crawling inside. That act of fluffing creates more air space between the fibers or feathers--air space easily warmed by your body.
• If the temperature looks as if it will drop below freezing, bring your boots and water bottle into the tent to keep them from freezing. In extreme cold, sleep with your boots and bottle.
• Before turning in for the night, nibble on something with high calories. The fuel your body now has to burn will help it stay warmer during the night. Old-timers used to mix a teaspoon or two of butter or fat with a cup of cocoa or stronger libation before hitting the hay. Same purpose, different method--the choice is yours.
• You can boost the efficiency of a sleeping bag in several ways. by wearing long underwear to bed (a fresh, dry pair), by doubling up sleeping bags, by using a sleeping bag liner, by sleeping wearing a parka and by sleeping in a tent.
• Sleeping on a thick and comfortable sleeping pad will also add warmth. Your body will lose more heat to the ground than to the air -- try lying on an unheated waterbed to get the idea. Closed cell foam or foam-filled inflatable is much better than an air mattress.
• When the temperature drops unexpectedly and you find yourself shivering in your sleeping bag, put on your rain gear (pants and jacket) to act as a vapor barrier and to hold in your body's warmth.