Apple

Apples are a common fruit found on Earth. They can be either red, yellow or green. After the Doctor regenerated he wanted an apple but didn't like it. Amelia Pond liked apples ever since she was young, when her mother would carve faces into them. She gave an apple with a carved happy face on it to the Doctor. Not long after (for the Doctor) but 12 years later (for Amy), the Doctor produced it in order to finally convince the older Amy that he was the same man she met as a child. (DW: The Eleventh Hour)

The Doctor claimed that he dropped apples on Isaac Newton's head. (DW: The Pirate Planet)