550 cord, paraline, paracord, parachute line, call it what you will, 150 feet of mil-spec parachute line should be a part of your gear.
As I think back over nearly 46 years of teaching survival skills and about the same amount of time beating about the bush, I don't think I have ever been without some parachute cord. I have used to to build shelters, catch fish, weave nets, make stronger rope, for emergency dental floss, as sewing thread, to retrieve water when I was cliff-bound and yes, parachute line has lowered me to the ground when I jumped out of an airplane while I was in the Air Force. Simply put it can truly be a life saver!
What is parachute line? Parachute line is made up of a tubular case containing seven pieces of thinner, nylon threads each of which can be further separated into three even finer threads.
The tensile strength of a piece of line is 550 lbs. The tensile strength of one piece of the inner thread is about 35 lbs.
You can buy parachute line in just about any color from many internet vendors or sporting goods stores. Or you can go to your local military surplus store where the predominant colors are white or OD green. I recommend buying white cord and then dying it bright red or orange so that you can find it if you drop the line on the ground or worse still, on snow. RIT fabric dye works well. Make a concentrated solution and then drop your parachute line into it and leave it there until you are happy with the color. Before you remove it from the dye pour in a cup of vinegar to set the dye and let it sit some more - a couple of days. If you don't do this, since nylon doesn't take up dye very well, the dye will come off in your hands.
Stronger rope can be made from parachute line by either twisting two ropes together or by braiding three or more pieces together.
As I said in the beginning, 150 feet in 25 foot lengths, should be included in your gear. There's no way to improvise a line from natural resources that comes close to the strength, utility and usefulness of parachute line. Check out http://www.shop.outdoorsafe.com/Parachute-Line-Parachute-Line.htm