Clara Oswald's TARDIS key

Clara Oswald held possession of a TARDIS key.

History
The Eleventh Doctor had provided a key to Clara some time prior to his participation in the Siege of Trenzalore. In anticipation of the conflict, the Doctor had the TARDIS take Clara home. However, as the TARDIS attempted to leave him behind, Clara grabbed hold onto the TT Capsule and inserted her key into the lock. As a result of extending its force field as it "dragged" Clara through the time vortex, the TARDIS returned to Trenzalore three hundred years later from the Doctor's perspective. (TV: The Time of the Doctor)