Potato

Potatoes were a vegetable on Earth, often used to make other Earth foods such as chips and crisps.

The Doctor was once imprisoned in the Tower of London with Sir Walter Raleigh, who kept going on about the potato, which he'd discovered. (DW: The Mind of Evil)

The Sontarans were said to look like potatoes on several occasions. (DW: The Two Doctors, The Sontaran Stratagem, SJA: Eye of the Gorgon, The Last Sontaran)

In 2075, the First Doctor, John and Gillian used potatoes as makeshift weapons to defeat the space pirates on Anastas Thrax's space station. (TVC: The Hijackers of Thrax) Later, in 1800, the Tenth Doctor similarly used potatoes in combat. Onboard an American schooner in the Caribbean Sea during the dying days of the Quasi-War, he used potatoes, turnips and molasses to create an organic mixture capable of clogging proton cannons. (DWBIT: Second Wave)