A couple of thoughts sleeping gear in various climates.
First, I do not recommend sleeping pills, you may need to wake up in a hurry. Under stress and tired, you should have no problem getting to sleep. If it's too cold for you to sleep, there is a good reason for it. Taking sleeping pills in that environment is asking for hypothermia or worse. It's about like a drunk passing out in a snow bank.
Same basic situation as drinking during extreme cold. Every spring in Russian cities, as the snow melts, they keep an eye out for the bodies of drunks that passed out in the snow during the winter.
If you're too cold, you simply need to get warmer, there's no getting around that. Then fatigue will kick in and you'll get some sleep.
Now, I've done a lot of backpacking, and a lot of my backpacking I've done without a tent, but never without a sleeping bag. There really is no substitute for a sleeping bag for any type of real cold.
For backpacking during 'normal times', I carry in my pack a Ridgerest style foam mat, a sleeping bag (North Face polar guard filled currently) with a goretex bivy, a poncho liner, poncho, mosquito net, 2 emergency style space blankets, and a tarp style space blanket. I also have a camo net I can bring, but it's not that necessary during 'normal times'.
A sleeping bag is no more tear prone than a poncho/mylar arrangement, much less so actually, especially with a good bivy sack.
If it tears, which is rare unless a person is wantonly careless, just fix it. The zipper and fasteners nowadays are very good. You can also modify your bag with velcro tabs for rapid opening under certain circumstances and/or to keep it closed in case the zipper fails.
You also have to work really, really hard to get a modern sleeping bag soaked, especially if your bag has a bivy, which you should get. You should also carry it in a tough, waterproof stuff sack. Many modern packs are made to carry the sleeping bag inside the pack.
The modern materials will also keep you warm even if it is damp/wet and they can be dried out a lot faster than the old materials.
More often than not, I'll just use the sleeping bag with a bivy, a Ridgerest style mat, and something to toss over it all and my pack, like a tarp or a poncho.
For a camp shelter, a square piece of canvas tarp is a tad heavier than a poncho but it works extremely well. It's very tough, won't be tossed about by the wind like something made of plastic or nylon, and you can camouflage it with spray paint if you want to. A piece of camo netting can be also be used and enhanced to supplement things.
Lay out your sleeping gear, lay your pack next to it along with maybe some local fire fuel you want to keep dry. Then just toss your tarp and/or net over everything.
It's fast to setup and pack up, and if you do this right, someone just about has to step on you to notice you.
Here's an interesting light sleeping bag. It's the Arktis Halo 3 sleeping bag designed for military ops. It's 2.5lbs and temp rated for 35F.
The Snugpak Jungle Bag is also pretty good
http://www.lightfighter.com/index.asp?PageAction=VIEWPROD&ProdID=199
I also carry a couple of emergency style mylar space blankets and a heavy duty space blanket that's like a tarp with grommet holes and is olive drab on one side. They have their uses and the additional weight is negligible.
One of the biggest problem with mylar is that it doesn't breath. The condensation from your own body will rapidly defeat attempts at keeping warm. Mylar's ability to warm is also rapidly defeated by any wind whatsoever, even the heavy duty ones.
I froze my ass off one windy, rainy night that I tried to rely upon an emergency style space blanket. The thing eventually started tearing to shreds so I tore it to pieces and then stuffed the pieces into my clothes. THAT actually worked noticeably better than wrapping myself in it.
Now, space blankets work well supplementing shelters. For instance, if your sleeping bag is a tad light for the weather, a space blanket tarp tossed over it helps out, as does an emergency style one used inside of the bag laid on top of you like a blanket. Space blankets also work well supplementing a poncho liner. A space blanket, if used right, can seriously supplement a poncho and poncho liner combo.
Space blankets are also good for the inside of a shelter used as a blanket and as a shelter liner, and any place where there is no wind, like inside of a vehicle. Mylar works best when there is some air space between you and it, and your body can breath. It also works well reflecting the heat from almost any source, like a candle.
Hammocks work well in the tropics, but in a cold environment outside, especially one with wind, a hammock's usefulness as a sleeping tool evaporates. A close cell foam sleeping mat will get you a lot further.
The poncho tent works OK, especially when the goal it to just keep the rain off of you when it's not too cold or windy out. The biggest problem is that the ends of the poncho tent remain open, allowing wind in. Rain can also be blown in.
For sleeping, I've used the poncho a lot more often as a sleeping tarp or as part of a bedroll. When it's not too cold and windy out, what works good for a fast sleep is to roll up in a poncho liner on the foam mat.
