of course this is a stupid idea as a planning strategy for so many reasons - I suppose it might be better than nothing as a last resort, BUT, one cold rainy afternoon when you hit a shelter and want a break before your last 8 miles to the next shelter and you are sort of cold - maybe chattering a bit (but if you get your bag out, you might quit for the day) - tuck your legs into a black plastic contractor bag - you will be amazed how nice and warm it makes you - learned this trick from triple crowner, "Sicily B"