Wearing a kilt has been a Scottish custom since the 16th century and is demonstrated in popular movies like Mel Gibson's 1995 award winning movie about Scottish hero William Wallace 'Brave Heart', and Liam Neeson's movie about an outlaw that wears kilts 'Rob Roy'.
Here is the list of Kilt Accessories usually worn in any Scottish traditional event, gathering and occasion:
Tartan Sash and Brooch. Sash is an essential accessory too; this is where the brooch is attached. Scottish brooch is usually Celtic and/or Triquetra design.
Sporran. This Scottish pouch plays as the pocket for Kilt wearers since most kilts do not have a pocket and is placed below the belt buckle area or the groin area and can be moved depending on the activity of the wearer. This can be either made out of animal skin, leather and others. It may also be Semi-Dress, Formal or Special based on what it is made of, design, texture, shade and purpose of wearing.
Highland Shirt. It is actually the traditional top wear kilt way back the 16th century but over the years it's been substituted with the shirt, tie and or/vest. It is a long sleeved dress and in most cases buttonless. Instead of buttons they use lace to tighten and loosen the fitting.
Shirt, Tie and Best. Shirt, Tie and Vest is the present day and formal wear for Scottish traditional gatherings and occasions like weddings, highland games among others. Generally, the color or design of either the shirt, tie or vest is coordinated to the color and design of the kilt.
Socks and Flashes. Normally, Scottish socks are knee high and in most cases made from wool and cotton or a mix of both and with kilt garter flashes in tartan just below the knee.
Brogues. This low heeled shoes or boots are built to be worn outdoor during the early 20th century but as years passed, it has been considered as formal wear. You will find a lot of brogue styles like the Closures, Full brogues (or Wingtips), Ghillie brogues, Longwing brogues, Quarter brogues and Semi-brogues (or Half brogues)
Belt and buckle. Most Scottish belts are wide (usually two to three inches) and made of leather (usually black) and buckles are mainly Celtic cross shaped along with other Celtic designs. The belt is amongst the most significant Scottish accessory because the top wear, kilt and sporran are on the pelvic area.
Balmoral and Glengarry headgear. Balmoral and Glengarry are named after a castle and a valley in Scotland and are two of the most common headgear and mostly black in color.
Fly Plaid. It is a large piece of cloth, the other half is draped on the left shoulder and the other half is belted and pleated on top of the waist. The color of the fly plaid is often the same color and fabric as the tartan and the kilt.
You will find a lot of debates on what is the genuine and complete Scottish costume, but the significant thing is we follow the custom by heart. And you may also not only buy but rent kilt accessories as well.