Yo-yo

A yo-yo was a round toy which shot up and down on a string.

While at the Time Lord Academy, the Doctor would skip classes to practice yo-yos and juggling. (PDA: Match of the Day)

The Doctor gave Mindy Voir a yo-yo in exchange for signing his copy of one of her albums. (CC: Helicon Prime)

The Doctor, realizing that the Time Lords had programmed his TARDIS to always return to Earth, compared himself to "some kind of a galactic yo-yo". (DW: The Claws of Axos) On Silurian Earth, a yo-yo was found in the cloak pockets on the Doctor's body. (NA: Blood Heat)

The Doctor's fourth persona was the one who most frequently kept a yo-yo on his person. Although he once used it to test local gravity (DW: The Ark in Space), he apparently used it primarily for fun. His skill with the yo-yo appeared to increase over time. (DW: The Android Invasion, The Brain of Morbius)

Leela spun the Doctor's yo-yo, thinking that it was part of the TARDIS' magic. (DW: The Robots of Death)

Romana once used the Doctor's yo-yo to test local gravity, and performed a complex figure-eight with it. (MA: The Romance of Crime)

It took Ace two weeks and tons of peer pressure to learn to use a yo-yo. (NA: Love and War)