Was part of the Redcoat's Pack in the item shop which is no longer available. Cannot be crafted and exists now only as a legacy item. Be careful when wearing these since most players will try and kill you just for your clothes.
Items in your backpack are not saved when you get KO'd.
When you are using hotkeys like shift+right click, items from backpack are managed separately and the game will not recognize items in your backpack for use as inputs/ingredients when crafting or building.
Part of the Redcoat Set, which includes: