A fishing rod was a tool used in the catching of fish.
The Fourth Doctor kept a fishing rod in his TARDIS. He used it when he went fishing on Tara. Prior to this he used it when he was with Izaak Walton. (TV: The Androids of Tara)
The Sixth Doctor later used it in several unsuccessful attempts to land Gumblejack. (TV: The Two Doctors)
The Seventh Doctor once tried to relax by fishing on the planet Adeki, but the attempt was frustrating enough that he ended up angrily snapping his fishing rod over his knee. (COMIC: Planet of the Dead)