Through my time playing Final fantasy 14, a certain aspect has been a small annoyance for me. If you go into a random dungeon, sometimes items will drop that you can only use once, like orchestrion rolls, hairstyles, minions and so on. But to figure out if you already have them, you have to enter your own inventory of said item to figure out if you already own it, or remember it by memory. This way it's often possible for people to unknowingly "ninja" items from players who don't have it by accident. Implementing a "you already own this item" or something similiar would be a big help for both players.