I have been interested in this area since I was a teenager, and I am now 57. I have tried various shelters over the decades, from the Sierra to near the Arctic Circle. I think the best thing you can do to provide emergency shelter in a wilderness situation is to be sure you always pack a survival kit when you go into the woods, and include in that kit two or three garbage bags. If you take them directly out of the box they come in and place them into a sandwich bag, then seal it, they will not open up and will stay nicely folded. They take up next to no room and weight nothing. Then, after you have made whatever windbreak or shelter out of whatever is available, you can line it with the garbage bag (slit open into a flat sheet with your knife), and crawl into another bag, to keep the wind off of you. I have done this in a driving rainstorm in Canada. Not comfortable, but survived.

The shelters shown here are not completely waterproof and windproof, unless you take days to construct it, and then it still is porous.

Some of the shelters in this article are great and will work well in a lot of different situations but a lot will take a good amount of time to construct if you want them done right. That means waterproof and big enough for you and your gear. Like Nelson said you have to have a good Personal Survival Kit (PSK) with you when you are out. That extra five or ten pounds will mean the world to you when you absolutely need it, trust me I've been there and done that.

This is a must know for outdoorsmen. But one must remember to make the shelter the right size. A shelter to large will lose all important body heat, but to small could mean an uncomfortable night.

The best shelter i stayed in was a space blanket under a hemlock tree in the snow, the hemlock had plenty of room to lay down, and the blanket kept me warm all night.

Short on cordage to bind your tripod? Try strips of Birch bark or pull up some spruce roots.

I spent three cold nights in a debri hut and have some tips for those considering trying one out. Take your time with the initial set up, and try setting it up underneath a tree because using leaves to cover the very top of your a-frame can be quite difficult, and the tree cover helps to block possible rain. Also I reccomend making your a-fram fairly tall. I misjudged how tall I needed to make mine and spent three nights waking up in the middle of the night with my head poking out of my roof and all my collected leaves scattered about. Very disheartening when all you have eaten for three days is a handful of soloman seal and a frog.