Green’s Dictionary of Slang

1. a tramp.

1955

N. Pulliam I Travelled a Lonely Land (1957) 231/2: coaster – a tramp.

2. a loafer, an idler.

1878		‘Rolf Boldrewood’ Ups and Downs viii. 75: ‘We’re from down the river,‘ said one of the fellows, a voluble, good-for-nothing, loafing impostor, a regular ‘coaster’.
1945		Baker Aus. Lang. 102: The scowbanker or skullbanker (1886), coaster (1878), sundodger [...] were other vagabonds who loafed in the outback or drifted from station to station.