What is an example of a metonymy?

From the Greek Word metónymia - "substitution of a name for another name", metonymy denotes a person or an object by using the name of another object which stands to the former in a close, typical or representative relationship. The relation between the two has to be generally know, e.g. saying, I want to buy a Styron does not mean I intend to buy the writer´s house in Connecticut, but a book by him. Get it now?