A razoo is a worthless coin, and the reference to brass differentiates it from gold, silver, or even copper, just to emphasise its worthlessness. I think it is one of the expressions troops picked up in the Middle East in the First World War, but I'm not sure. It's not in the Macquarie Dictionary, which is rather surprising.

Plonk is a slang reference to wine, and usually implies a cheap, inferior grade. One of the stories ascribing its origin is that it is the sort of grog that makes you fall down plonk! It is possibly derived from blanc, or white (as in wine).