You can use this when the minibuffer expects you to type something (caveat: does not work with ido, but obviously you can always exit it, for example, Cx Cf). You can also use it in regular buffers.
(defun insert-filename-or-buffername (&optional arg)
"If the buffer has a file, insert the base name of that file.
Otherwise insert the buffer name. With prefix argument, insert the full file name."
(interactive "P")
(let* ((buffer (window-buffer (minibuffer-selected-window)))
(file-path-maybe (buffer-file-name buffer)))
(insert (if file-path-maybe
(if arg
file-path-maybe
(file-name-nondirectory file-path-maybe))
(buffer-name buffer)))))
(define-key minibuffer-local-map (kbd "C-c f") 'insert-filename-or-buffername)
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