While I can't be authoritative, I doubt very much if it's Aussie or any other foreign source. My grandparents used this expression, and I can't imagine that in their young days (1885-1915) there were any imports into the U.S. from Oz, linguistic or other. [OK, let me have it, all ye antipodean authorities.] "Kit" surely refers, as you note, to an assemblage or collection; my guess is that "caboodle" (as I have seen it spelled) is made up from "bundle".