Heard first on Gold Coast, Australia. Pluggers are thongs, slip ons, flip flops etc. They are specifically the type of thongs that are a thin sheet of rubber and a "wishbone" shape of rubber protruding from the thin sheet that goes between your toes. This wishbone piece of rubber is held to the thin sheet of rubber by "plugs" that protrude through the thin rubber sheet from top to bottom. You can have single pluggers or double pluggers or maybe more, this number comes from the number of plugs for each wishbone anchoring point on the bottom of the thin sheet.
You better put on your pluggers as the road is very hot.