"Over the last six months I've been keeping track of what I eat and am surprised to see that my average daily calorie intake is 1,405 Kcal ... I take an average of 30mins exercise a day by fast hill walking for a mile and a half." Welcome to the club! I'm another one. The experts claim that I need 3000 calories/day at my height (6'4"), weight and activity level (a field naturalist); my basal (sleeping) metabolism is supposed to be 1600 calories/day! In fact, I maintain my weight steady with only 1500 calories/day. But relax, it's perfectly possible to obtain all the nutrients in RDA quantity on as little as 1000 calories/day, and with an essentially natural diet to boot. See http://sankey.ws/diet.html for some notes on how to do it. As far as outdoor sleeping goes, order from Mountain Equipment Coop. They've got stuff I can use to 40 below.