The concept of metonymy is difficult to explain. I think Jakobson's use of the word contiguity is rather misleading, since it implies two things laying side by side. Metonymy is a substitution of one word for another. It thus works on the axis of substitution, despite what Jakobson seems to be saying. The relation between the two terms is one of actual connection. Thus we might say "Tin Pan Alley" instead of "popular songwriters of the 1920s." (I tried to use this example, but my students are too young to have heard the expression). Many metonymies are based on places:

Nashville = country music industry
Wall Street = the stock market, the financial industry
Madison Ave = advertising
Detroit = auto manufacturing

There are also the classic cases of effect for cause, cause for effect, container for the thing contained, part for whole and whole for part. There are metonymies based on clothing: the suits, white hats, etc... I give examples of these to my students, but they seem curiously unable to generate examples of their own.

It's not clear why Jakobson thought of metonymy as involving the combination of words rather than the substitution of one expression for the other. Perhaps the idea of "contiguity" led him to make an analogy between words lying next to each other in a sentence and the relation between elements in the real world. The White House is a metonymy for the Administration, but the relation between the White House and the Administration is not analogous to the relation between a noun and a verb in a sentence, as far as I can see.

Either I am correct about this, or I am incredibly obtuse and am not getting it. The fact that I've never been able to convince another human being of this idea leads me to think I am obtuse. Yet I have never heard a satisfactory refutation of my theory either. My hunch is that Jakobson's theory made people forget what a metonymy actually is, that now, when they refer to the concept, they are referring to his article and not to real examples of metonymies in language usage. Thus my objections don't make sense to anyone else. It's like trying to argue someone out of the proposition that a dog is not the opposite of a cat.