Green’s Dictionary of Slang

1. (Aus.) a packhorse [abbr.].

1875		Wood & Lapham Waiting for Mail 59: The boys took notice of a horse, some old packer he looked like.
1890		Argus (Melbourne) 7 June 4/1: The Darling drover with his saddle-horses and packers.
1941		Baker Popular Dict. Aus. Sl.

2. (drugs) a thin stick, typically a chopstick, or a piece of metal coat hanger, used to pack a cocaine pipe.

1992

T. Williams Crackhouse 40: There are also tools [...] a wire ‘packer’ fashioned from a clothes hanger, a metal scraper from a broken umbrella spoke – and her pipe. [Ibid.] 150: packer wooden stick or chopstick used to pack scree into pipe.

3. see fudge-packer under fudge n.