I used this pattern and some leftover sock yarn, as Kristi suggests.
My execution of her pattern was not perfect, but the product is serviceable.
The fun new technique, which I haven't quite mastered, was i-cord all around the pouch--picking up and knitting while i-cording, which makes a very strong pouch and a very well-attached cord.
If I made another, I'd make a flap and a button hole. (But it is hard to imagine one would need more than one Nano Necklace.)