The Doctor's psychic paper
From Tardis Wiki, the free Doctor Who reference
The Doctor, throughout their lives, carried a card of psychic paper.
History
The Second Doctor was given psychic paper while employed as an agent by the Time Lords' covert organisation, the Celestial Intervention Agency, which had developed the technology. He and the Time Lady Serena used it to attend the Duchess of Richmond's ball to keep an eye on the Duke of Wellington. (PROSE: World Game)
Just prior to Earth Death in the year 5,000,000,000, the Ninth Doctor used psychic paper to pass himself off as a guest, under the name "the Doctor", with Rose Tyler as his "plus one to the steward of Platform One. (TV: The End of the World)
