Scott in kilt with sporran in front of it
The sporran was a traditional Human clothing accessory, typically worn by Human males of Scottish descent while wearing a kilt.
It was in the form of a pouch or purse, and was affixed to a chain around the wearer's waist. The sporran was generally worn in front of the kilt, often had two or three tassels in front of it, and could be used to contain items — such as money, for example.
A sporran hangs with Scott's red and black kilt on the wall of his room
When engineer Montgomery Scott entered the drinking competition with Tomar, one of the Kelvans in Human form, a number of Scottish objects could be seen hanging on the wall of his room — such as a kilt, sporran, targe, and bagpipes. (TOS: "By Any Other Name")
Scott was also allowed to wear a sporran as part of his dress Starfleet uniform to reflect his heritage. (TOS: "Is There in Truth No Beauty?", "The Savage Curtain")