A total of 23 Cosmetic Items are available in Atlas Fallen. They can be obtained in several ways:
Once you collect all of them, you will unlock the "Feeling Fancy" achievement / trophy
Buckler
Ever Burning Sun PauldronIt can be bought from the Traveling Vendor.
Helmet of the lost Knight of BastengarIt's in the "Mine and... yours" Treasure Chest.
Jousting Shield: Sun KingdomTo unlock this chest you have to complete the Sealing Totems (Caladrias #4).
Straw CoverIt's a reward for completing the "Food for the People" side quest.
Griffin Chestplate (Red Chest)You need the "Crush" gauntlet upgrade to open this chest.
Helmet of a Knight of OldIt's a reward for completing the Forgotten Path (Bastengar #1).
Helmet of a Lothville KnightYou will get it when you complete the "Valery's Trail" side quest.
Jousting Shield: Eternal Sun (Red Chest)You need the "Crush" gauntlet upgrade to open this chest.
Jousting Shield: Lothville
Lothville Crown
The helmet of a Knight of BastengarTo unlock this treasure you have to complete the Sealing Totems (Bastengar #1).
True Guardian HelmetTo unlock this treasure you have to complete the Sealing Totems (Bastengar #2).
Iron MaskIt's a reward form completing the side quest "The Imprisoned Priest".
Jousting Shield: Hawk
Jousting Shield: Knights of BastengarYou have to complete the Sealing Totems (Monsalar #12) to unlock this treasure.
Jousting Shield: Lothville FlowerIt's in the "Holding heaven" Treasure Map Chest.
Jousting Shield: Sun and Moon
Lion ChestplateIt can be bought from the Vendor.
Rays of the Sun ChestplateIt's a reward for completing the "Poetic Muse" side quest.
Solar ChestplateTo unlock this treasure you have to complete the Sealing Totems (Monsalar #9).
A simple, small metal shieldYou have to complete the Sealing Totems (Black Alms #1) to unlock this treasure.
Owl Chestplate