It could be that you don't need to know about survival clothing. You probably always hike with spare clothing.
Perhaps you never go out into the wilderness for overnight stays, but just for day hikes.
Or you are just like my wife who happens to pack everything but the kitchen sink and more than once that extra preparation has saved our skins.
Nonetheless, hundreds of people die or come close to dying every year from exposure. They thought they were prepared. They didn't expect their clothes to get wet from falling in a stream, they didn't think they'd be out there for the night, or they get lost for days.
Coming down from Mount William in Halls Gap in Victoria Australia once, I met several young men in t-shirts on their way up, determined to get to the top. They had no gear, and not enough time, but they probably made it there by sunset anyhow. They also certainly didn't make it the eleven miles back to their car before dark. It was below freezing that night, so I imagine they were uncomfortable at best.
I remember a colleague of mine who after having a domestic with his lovely wife decided to go for a walk in the many bush paths in the Great Ocean Road and got lost for two days and he was an experienced bush walker. Thank God he found his way out eventually but he only had a jumper on him and lost 8 kilos in those two days. It always is a good idea to be prepared and prepared well.
Quick Survival Clothing
What survival clothing could the young men and my colleague have made in that situation? One of them did have a light jacket. He could have used his t-shirt as a hat (a lot of heat is lost through the head) and filled his jacket with the fluff from the cattail seed heads for insulation. (Cattail down was once used to fill those old orange life preservers.)
Insulation is the important principle here. You can stuff a jacket, shirt, sweater or pants with dry leaves, milkweed down, bracken ferns or almost anything that creates a lot of “dead air space.” It's better if you have two layers to sandwich it between, but being itchy is better than being frozen in any case. Temperatures plummet and maintaining body heat is essential.
In an emergency, you can also use the flat leaves of cattail plants to weave a vest that will block the wind. Two bread bags full of milkweed down or other silky plant fibers make warm mittens (tie them at the wrists). A plastic bag full of the same could be tied onto your head as a hat.
Usually, you'll do better to look first at what you have, before looking to kill animals for their skins, or weave grass skirts. A sleeping bag, can double as a coat – just wrap it around you. Socks can be mittens, and garbage bags can be made into snow pants.
A garbage bag can also be used as a raincoat. Otherwise, tie bunches of grass tightly together along a string or strip of cloth, and then wrap it around your shoulders. This will repel light rain but no more. You can fashion a rain hood of birch bark as well.
In the desert you can make a sun-hat of large leaves, like those from a fan palm. String some together to wrap around your shoulders to prevent sunburn, or just wrap a t-shirt around your head especially at night.
You'll probably never have to use animal skins for survival clothing. You might never lose your shoes and need to glue tree bark to your feet with pine sap, for hiking. Still, knowing how to improvise a few basic pieces of survival clothing can make you more comfortable, and possibly save your life.