Green’s Dictionary of Slang

a regular or heavy drinker.

1873		Sl. Dict. 250: Peggers people who constantly stimulate themselves by means of brandy and soda-water.
1882		Sydney Sl. Dict. (2 edn) 7: Peggers - Great drinkers of brandy and soda.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1895		C. Crowe Aus. Sl. Dict. 57: Peggers, constant drinkers of brandy and soda.