Satsuma

Satsumas were a type of Earth citrus fruit. Sometimes called Christmas oranges, they were commonly given for Christmas in Great Britain, similarly to tangerines. The Tenth Doctor said, "...doesn't that just sum up Christmas? You go through all those presents and right at the end, tucked away at the bottom, there's always one stupid old satsuma." (TV: The Christmas Invasion)

Uses of satsumas
Doctor Ogron gave a satsuma as a gift of peace to Major Tamasan. (AUDIO: Planet of the Ogrons)

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 when the Sycorax leader, in violation of the rules of combat, prepared to attack him from behind. The switch opened the hull under the leader's feet, and he fell thousands of feet to his death. (TV: The Christmas Invasion) The Doctor soon mentioned the satsuma in his diary, (PROSE: ) and it was later found in Brockley in early 2007 and stored in the Leamington Spa Lifeboat Museum. (GAME: Security Bot)

During an explanation on how wormholes work, the Eleventh Doctor used a satsuma to represent Earth, which he handed to Mae Callon. Later, as they were surrounded by Wanters, Mae threw the satsuma at the group, distracting a portion of them. (PROSE: Shroud of Sorrow)

Behind the scenes
Satsumas are referenced in Attack of the Graske  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".