How can one clear the kill-ring? C-h v kill-ring produces
a read-only file, so one cannot edit it there.
M-: (setq kill-ring nil)
If you use Icicles (http://www.emacswiki.org/cgi-bin/wiki/Icicles), you can
remove specific kill-ring entries interactively. `C-- C-y', then:
* `S-delete' individual entries to remove them from the ring.
* `C-u S-delete' to delete all kill-ring entries that match your current
minibuffer input. This lets you filter the kill-ring, purging it of entries that
match given patterns. If the minibuffer is empty, then this empties the
kill-ring completely.
[BTW: `C-h v' puts you in the *Help* buffer, which is read-only. You can always
toggle a read-only buffer using `C-x C-q' to make it writable. Making the *Help*
buffer not read-only will let you edit its text, but that doesn't change the
value of the variable `kill-ring'. *Help* just displays the variable's value.]