A regularly-occurring event in Doctor Who stories is the Doctor pulling vast quantities of items out of his pockets, far more than they would seem capable of containing. The gag fits with the nature of the TARDIS, which is also bigger on the inside than the outside.
So when did this property of the Doctor's pockets first appear? The earliest television serial in which I can remember it appearing is "Genesis of the Daleks," in which the Doctor is asked to empty his pockets when he is captured in the first episode. That's early Tom Baker, but I think it must have originated earlier, because I think that I can recall either Patrick Troughton or John Pertwee mentioning the pocket gag at a fan event I attended.