use the 1/4 lb, $20 SOL 2 person Emergency Bivvy bag, a mylar product, and to avoid the horrendous condensation that such a bag always produces, I use half of a 1 lb, $10 bag of "double layer" absorbent painter's drop cloth from Wally's. It's 12x8 ft, but you only need half of it to make a 3x8 ft bag. I used duct tape to mount zippers all around all 4 bags, so that I can open them flat if I see fit.. I also carry a couple of 3x8 ft bags made out of bugnetting. they total 1/2 lb. One can be stuffed with debris and used as a sleeping pad. Up on such a pad, the 2 bags, tented over a ridgeline, will let you sleep ok at 40F, in office clothing. If you'll stuff the area between the 2 bags with dry debris, it will handle 34 F and rain. If you get a lot of wind, you can use the re-usable (if you're careful) blue masking tape to mount a couple of widths of aluminum foil down the windward side of the outside (mylar) bag, and it stops the wind just great. I normally also a hammock made out of 1 lb monofilament gillnetting, so that I can get up off of the mud and snow, up in the breezes for summertime, some cordage and stakes. 2.5 lbs. I also carry a balaclava, gloves and liners, longjohns, 3 pairs of medium weight wool socks and a spare set of nylon socks, a UCO candle lantern and spare candle (beeswax only) a boonie hat, and a pair of trekking poles. 3 lbs total that get me sleeping ok at 20F, given the debris-stuffing. I can wear the bags as a poncho, too. So I can be ok at 0F while moving. I can use a discrete Dakota fire pit to heat water bottles or rocks, or do exercises in the bag. and handle another 10F of cold. It's going to warm up a bit by noon, and this gear can be rigged for use as a Korchanski supershelter, for use with either a Siberian fire lay's ability to project its heat all in one direction (up to 2m) to protect my synthetics from popping embers. So you can either hike, have a fire, or exercise all night, use the candle or heated rocks/water in the early morn and then use the sun and greenhouse effect to sleep from 11 am to 5pm, given a sedative, earplugs and sleep mask. That is very little in the way of cost, bulk or weight, to handle such a wide range of temps and condtions. The absorbent stuff does soak up water very quickly and is practically ruined by it. It also catches fire pretty easily and burns about like toilet tissue.