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Frequently used in the imperative, as rattle your dags, the New-Zealand and Australian slang phrase to rattle one’s dags means: to hurry up, to get a move on.

For example, the New-Zealand lexicographer and dictionary editor Robert Burchfield (1923-2004) mentioned this phrase in a review of The Macquarie Dictionary, published in The Age Monthly Review (Melbourne, Victoria, Australia) of March 1982 [page 11, column 4]:

A young New Zealand niece of mine recently said to her English host, “Well I suppose I had better rattle my dags and be off”. “None of your turnip language here”, was the stern reply.
Australian English has its engaging and innocently earthy seams that will continue to make it seem to be one of the more exotic members of the mother tongue.

The following explanations are from the Australian National Dictionary Centre (Australian National University, Canberra, Australian Capital Territory):

Dags are clumps of matted wool and dung which hang around a sheep’s rear end. When a daggy sheep runs, the dried dags knock together to make a rattling sound.

The earliest occurrences of to rattle one’s dags that I have found are as follows, in chronological order—this phrase seems to have originated in New Zealand:

1-: From The Pagan Game (London: Robert Hale; Christchurch (New Zealand): Whitcombe & Tombs; 1968), a novel by the New-Zealand author Gordon Cyril Slatter (1922-2002) [page 161]:

I’m not overstruck on that new cop.—Told me to rattle my dags out of there.

2-: From Awatea (1969), by the New-Zealand playwright Bruce Mason (1921-1982)—as published in The Healing Arch: Five plays on Maori themes (Wellington (New Zealand): Victoria University Press, 1987) [page 220]:

Brett, urgently: We’ve got to see that letter. First. Get her back.
Jameson, cupping his hands, bawling: Ma! Hey, Ma!
Gilhooly, faintly, off: Where’s the fire?
Jameson: Come back here! Important!
Gilhooly, indistinctly: Later!
Jameson: The P.O.’s on fire!
Gilhooly, faintly: Nuts!
Jameson: It’s about Matt! You have to see me first! At the double! Rattle your dags!

3-: From Not Here, Not Now (London: Robert Hale, 1970), a novel set at the University of Otago, Dunedin, Otago, New Zealand, by the New-Zealand author Daniel Marcus Davin (1913-1990) [page 328]:

He picked up the bottle from the floor, emptied it into his glass and swallowed the lot. It took effect at once.
“I’ll be with you in two shakes of a lamb’s tail.” Odd to use a favourite phrase of his mother’s in a moment like this.
“You’d better rattle your dags, then.”

4-: From Tom Horton’s column, published in The Honolulu Advertiser (Honolulu, Hawaii, USA) of Thursday 14^th November 1974 [page A-3, column 1]:

Is Australia, a former penal colony, now more stable than the U.S.? Passing through town is Dr. James Cairns, Australia’s deputy prime minister and the equivalent of the office we have trouble filling—vice president . . . Fran McFall, covering Hawaii for the New Zealand South Pacific Trade News, suggests that visiting Aussies may have cackled at recent item here about bureaucrat named Dags—Dept. of Accounting and General Services. But for different reason. Down under, dags refers to unsanitary substance on south end of a north-bound sheep, hence the Aussie slang for “get a move on” is “rattle your dags,” which is good advice for DAGS . . .

5-: From Pallet on the Floor (Palmerston North (New Zealand): The Dunmore Press Ltd., 1976), a novel by the New-Zealand author Ronald Hugh Morrieson (1922-1972) [page 135]:

“Let’s get moving. Rattle your dags, McGhee.”

6-: From Weasel Words (New York: Oxford University Press, 1979), by Philip Howard [page 133]:

Pommie: There are the outback words from the backblocks to the back of beyond and Woop Woop, your expressive slang for a remote rural town or district. There is a big range of words connected with the bush. We have the bush-baptist, the bush carpenter, and the bush-lawyer, all of whom I wish to avoid, if possible. Nothing personal, you understand. There is your bonzer bushman with his bushcraft. There is the bushfire, of course, and the bush telegraph. You can get bush-sick, or just go bush. It is remarkable how much bush has come into English from your country.
Ozzy: Rattle your dags, man. I’ll bet you a dollar you still don’t know your jackaroo from a rouseabout.
Pommie: On the contrary, I am impressed by the conspicuously large group of words in Australian English that show how important sheep are.