Green’s Dictionary of Slang

(Aus.) a pack.

1905		Duke Tritton’s Letter n.p.: I rambled over to the Rubbity Dub and had a pint of Oh My Dear. In fact I had several and finished up in the dead house, broke to the wide. But they left me my Willy Wag and gave me a bit of tucker.
2002		Pete’s Aussie Sl. Home Page 🌐 willy wag: a swag.