Kevlar cord comes pre-wrapped in 20 foot spools, making it quite handy for tossing into a kit. Its compact size means that it can be wedged into even pocket sized survival kits. It weighs practically nothing too, so it's doubtful that it will weigh you down.
As cordage goes, kevlar cord probably will not be your very favorite. It has a plastic feel to it and is only so-so for knot tying. It's yellow. 135 lb test is strong enough for many survival tasks, including most primitive shelter building, but it's obviously not strong enough to support body weight or more.
But, if you need a lot of cordage in not a lot of space, Kevlar cord may be your best bet. The spool of 20 feet is roughly 1.5 inches by 1.5 inches wide and long, and about .4 inches thick. Size wise, the individual cordage strands are on par with a thick thread.
Due to the thinness and strength, the cord also makes for a pretty good improvised saw for cutting through plastics and similar materials.
The kit that the SEALs recently put an RFQ out for lists kevlar survival cord as its main cordage, though they require a higher 188 lb breaking strength.
Vigilant Gear has spools for $4 a pop >