Satsumas were a small variety of tangerine commonly found in Christmas stockings in Great Britain.
History
A beggar boy who was kidnapped by a Graske in 1883 said he was "saving up money for a satsuma". (DW: Attack of the Graske)
Following his victory over the Sycorax leader in a sword fight in 2006, the Tenth Doctor found a satsuma in his pocket and threw it against a switch on the hull of the Sycorax vessel. The Sycorax leader, who, in violation of the rules of combat, was about to attack the Doctor from behind and kill him, had the hull under his feet open up, and fell thousands of feet to his death. (DW: The Christmas Invasion) The satsuma ended up being kept in Leamington Spa Lifeboat Museum along with a Sycorax sword. (WEB: whoisdoctorwho.co.uk)