This is the same model of case used, and redressed, by the Prop Dept. to become a standard Starfleet-issue carry case. The found item used was actually an audio cassette carry case, called the "Dynasound Organizer Cassette Tote Case", and was widely available at the time the show was on the air. It was also used extensively on set during filming for DS9. I plan on detailing it to reflect the earlier version of medkit that was used on TNG, or perhaps the engineering kit (second last pic; last pic is a screencap from a DS9 episode, though I don't believe they changed the detailing of the cases for the later series).
