The Doctor's fob watch

The Seventh Doctor wore a fob watch when he regenerated. It was among the personal effects fraudulently collected by Chang Lee after he found the dying Seventh Doctor, but he later returned it to the Eighth Doctor, who took to wearing it once again. (TV: Doctor Who)

Behind the scenes
In The Forgotten, the Eighth Doctor claims that he was only half-human during the events of the TV Movie due to having used a "half-broken Chameleon Arch" on himself to fool. Given the prominence of shots of the Doctor's fob watch in the TV movie, which were not intended to serve a specific plot purpose other than emphasise the Doctor's association with time, the implication seems to be that this watch was actually a biodata module, as seen in Series 3 of revived Doctor Who. However, this is not made explicit. Additionally, many other accounts present different interpretations of the Doctor's infamous "half-human" comment, with the Chameleon Arch theory only being one possibility.