Erin talked about paracord a couple episodes back on the Gunblog Varietycast. Because I think paracord is exceptionally cool, I'm going to expand on that a bit.
Paracord is short for "parachute cord" and is also known as 550 cord. It was originally designed for the suspension lines on military parachutes. The 550 designation comes from it being rated for 550 pounds.
Common paracord consists of 7 inner strands rated at 50 pounds each and an outer sheath rated at 200 pounds. Solid nylon construction makes it water resistant, rot resistant, and slightly elastic.
There are two things that make paracord particularly handy. The first is the ability to separate it into its component strands: the inner cords can be removed individually and used for trapping, sewing thread, makeshift fishing line, or anything else that calls for light line. The outer sheath can still be used as cord for tent lines and other securing.
The second neat feature of paracord is the plethora of ways it can be carried. Everyone has seen paracord bracelets, and the same pattern can be expanded into a belt. Paracord rifle slings work well for hunters. It makes excellent boot laces. I have about 3 feet in my pocket in a monkey fist knot. It is also inexpensive enough to be disposable.