Before you book your Aus plane ticket, you may be saddened to know the UK and Aus Woolworths are completely unrelated [1] and very different beasts :(

The Aus/NZ ones are much more like supermarkets, I went to one in NZ and sadly found Pick-a-mix was not a focal point at all.

[1] http://en.wikipedia.org/wiki/F._W._Woolworth_Company