The C-Fish was a type of music player developed in the 2020s. It was portable and had tiny earphones.
When Jack Harkness was a Time Agent, he stored a C-Fish X20 in a locker at King's Cross, just in case he needed it. When he was working for Torchwood Three, he decided to get back the C-Fish in 1967, just because he wanted to listen to some music. (PROSE: Trace Memory)