Another tip, people down on their luck may be given supermarket vouchers by charities such as the salvation army which they can then spend on groceries with the restriction that no tobacco or alcohol be bought with them. Consequently at the checkout there will be people hanging around offering to sell their vouchers for a discount. I bought $50 of vouchers for $30 the other day and everybody was happy, except the salvation army perhaps.
And yes op-shops in Australia are where charities sell donated goods, I think they are called thrift shops in the USA. Apart from clothes they are also good sources for books and cd's, some people trawl them for rare vinyl.