Not Worth A Plug Nickel Meaning

(chiefly US, idiomatic) Having no or almost no value; worthless.

Example: 1975 Sep. 25, Vincent Canby, "Redford a CIA Eccentric in Three Days of Condor" (film review), New York Times, p. 60:
  In the screenplay by Lorenzo Semple Jr., and David Rayfiel, Turner very early on stumbles upon the existence of a kind of super-C.I.A. within the C.I.A., after which his life is not worth a plug nickel.