"The term swag similarly has its origin in thieves’ slang. It originally referred to a thief’s booty or plunder, but by the middle of the nineteenth century it was used to describe the collection of personal belongings wrapped up in a bedroll, as carried by a bush traveller. This is the beginning of the swagman tradition.
"Most of the recorded terminology has to do with the organisation and administration of the convict system, and disappeared with the demise of that system. Many of these, however, are included in the Australian Oxford Dictionary because of their importance to Australian history."
—from the article