Green’s Dictionary of Slang

plastic; esp. in placky bag n., a polythene carrier bag.

1994		I. Welsh ‘Stoke Newington Blues’ in Acid House 40: [He] came out stiffed in a placky bag.
2000		N. Griffiths Grits 131: Colm [...] pulls a pot of milk from undurr the table, wahn o’ those placcy two-pint jobs. [...] 296: Sam loops the wire off over the fox’s ed with the barrel uv is placky gun.
2006		D. Mitchell Black Swan Green 206: Le Grand Meaulnes was wrapped inside two Martks and Spencer placky bags.
2012		(con. 1980s) I. Welsh Skagboys 169: He held a wee placky bag fill ay white powder crumbs up.