I made these Monkey's Fist zipper pulls with 2mm trot line(Type I paracord also works good for these). I made an overhand knot at the starting end of the fist and tucked it inside for use as a core before tightening it up. I've seen small ones like this used for earrings before.
When attached to a zipper, they make it easier to open bags, backpacks, jackets, etc., especially when wearing gloves. And if you have a lot of metal zippers on a bag/pack, they can tend to make a lot of racket as you walk, so replacing them with cord helps to cut down the noise.
Shown attached to a Maxpedition Cocoon pouch.
I've taken some photos showing the adding of the loop to the monkey's fist. Once the fist is made and tightened with just the single strand left, you work backwards pulling enough of the end strand back to make a loop. Work that amount back thru the fist (just like you worked the slack out of the fist when tightening it). I take it thru to the center of the second set of turns. Then trim the single strand off the fist and tuck it into the fist, a clay stylus is useful with such a small monkey's fist.