Part of the standard issue US Molle II system: the tourniquet pouch.
These are in OCP/Multicam.
These are designed to fit CAT Tourniquets.
NSN: 8465-01-683-4707
They feature a single molle strap on the back to hook onto your gear, and has Velcro closures for fast access.
These will be from a variety of makers, but all are genuine US Government issue and in excellent shape.