Equippables are a type of item that can be equipped to your pets, allowing personalization options. They come in many shapes, sizes, and varieties. These items can be purchased from NPC shops, obtained via site events, bought from the OotS Shop, and are sometimes released as site-wide freebies.
A full list of current equippables can be found here.
Species-Specific Equippables[]
Some items are species-specific, meaning they can only be equipped to the species they are meant for. These are mainly shop items and are identified by a small icon found on the top right corner of the item box in shops. Ineki only equippables display a 
icon. Drasillis only equippables display a 
icon. Kelphi only equippables display a 
icon.
Items obtained through events, the Out of the Shadows shop, and site-wide freebies are able to be equipped to all species. (Kelphi compatibility will be slowly done in batches for previous OotS).
Avatar Equippables[]
Most equipped items only show up on a pet's profile image, but some items will display on the pet's avatar image as well. Items with this feature are identifiable by the [Equippable, Avatar] tag underneath their thumbnail image.
At first, there was only a small selection of items that were compatible with forum icons. As of Feb. 2015, the selection of avatar equippables has grown considerably.
In March 2015, avatar background equippables were introduced. When equipped to a pet and the pet is used as the user's forum avatar, the item replaces the normally white background on forum avatars.