Wood

Wood was an organic material deriving from trees. This was a widely-known fact. (TV: City of Death) "Woods" was also a word used to describe forests, spaces with large quantities of trees.

Wood went into flames under extreme heat. (TV: The End of the World) Some objects that were made of wood, such as cricket bats, required regular application of linseed oil for proper maintenance. (TV: Castrovalva) Beavers could chew through wood. (PROSE: Wetworld)

The Doctor's sonic screwdriver was ineffective on wood. He was rather embarrassed of this. Once, when the Eleventh Doctor was battling Androzani trees, he complained about the aliens being made of wood, rendering his sonic useless on them. He again found himself in this predicament when facing peg dolls. (TV: Silence in the Library, The Hungry Earth, The Doctor, the Widow and the Wardrobe)

Many of his companions ridiculed the Doctor for his TARDIS exterior being seemingly made of wood. (TV: Smith and Jones, Meanwhile in the TARDIS, The Bells of Saint John)

Uses
Wood was often used to start and/or maintain fires either in a fire pit (TV: Countrycide, The Sound of Drums) or in a fireplace. (TV: The Girl in the Fireplace)

Books, gallows and spoons were all made from wood. (TV: Silence in the Library, Mona Lisa's Revenge) Doors were also made from wood. (TV: Silence in the Library, The Hungry Earth) One of Banquo Manor's doors were described as having been made of "strong wood." (PROSE: The Banquo Legacy)

Centuripedes required oak wood to build a pod to transport their eggs. (TV: The Last Oak Tree)