My understanding is that "Matilda" is the hiking staff. "Waltzing Matilda" is the act of hiking along, where one is figuratively waltzing with Matilda.

Perhaps Matilda is a pack or a bag rather than a staff, but unless it's something you've got your hand around the idea of waltzing with it gets a little more remote. The syntax of the lyric "Who'll come a'waltzing Matilda with me" pretty much precludes the phrase "waltzing Matilda" from being an object--Matilda itself would be the object, waltzing would be what you do with it.

I seem to remember "jumbuck" being a lamb rather than just any age sheep.

In American English, I believe "stockman" would be "rancher."