A sprite pendant is an item that Sburb players unlock after some amount of progress through the game. It allows the bearer of the pendant to summon the associated sprite whenever they wish, allowing the sprite to, for instance, be taken beyond the gates to other lands or down into the depths of the planet. The pendant works for whomever holds the pendant, not just the player associated with the sprite. Typically, when a sprite is no longer needed by the player, the sprite is given its own pendant. This is primarily a symbolic gesture, but it does protect the sprite from being randomly summoned away. Summoned sprites appear to come out of the pendant, but John notes that he is "pretty sure they don't actually live in there". They can, however, be temporarily "stored" in the pendant, as seen with Erisolsprite. It's implied Davesprite used the pendant in this way to escape harm while fighting Jack Noir with his Bro.
The pendant is presented to the player in person - they don't automatically get the pendant when they reach the correct rank on their echeladder. John receives his from Nannasprite when he was an Ectobiolobabysitter, but Nanna tells him "You should have returned sooner! I could have given you this boon at a much lower rung."