Credit cards (7)
I believe the answer is:
'credit cards' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for plastic that I've seen before include "non-metallic material" , "means of deferring payment" , "Scalp it badly to make a synthetic material" , "Fashionable - substitute for wood or metal" , "Clasp it (anag.)" .)