Satsuma

Satsumas were an Earth citrus fruit. Sometimes called Christmas oranges, they were commonly found in Christmas stockings in Great Britain.

Uses of satsumas
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. He fell thousands of feet to his death. (TV: The Christmas Invasion)

Behind the scenes
Satsumas are referenced in NOTDWU: Attack of the Graske, a story this wiki does not consider to be a valid DWU source as it has multiple endings, which we cannot qualify through any mechanism which is the "correct" or "canonical" one.

In Attack of the Graske, a street urchin who was kidnapped by a Graske in 1883 said he was "saving up money for a satsuma".