Shomer-Tec Zip Stash
Shomer-Tec's Zip Stash attaches as a zipper pull, and contains a slide-out compartment with 2" x 0.35" x 0.35" of space for storing your...uh...clipped fingernails? A rolled up slip of paper with important phone numbers on it in case you lose your phone? Maybe a single bill or a piece of gum, but at that size, the Zip Stash can't even concealed carry a key or a joint for me. Sure, no one will ever guess you've got goods stored in your zipper, but so too might you never guess what goods you've got that are tiny enough to make it worth storing them there.
But for those still gung-ho on Zip Stash ownership, the zipper pull has a matte black exterior with low noise and glare properties, so it shouldn't stand out in any way. The attachment cord is Kevlar encased in a black HDPE extruded cover so the Zip Stash should stand up well to those with overenthusiastic zipping habits.