Of all the literary tools available, I think Metonymy (and its step-child, Synecdoche) can offer the most creative means for having fun while writing. Of course, it takes a little untangling to understand exactly what it is and how it differs from similar figurative language tools.
According to my handy Oxford Concise Dictionary of Literary Terms, Metonymy is:
"a figure of speech that replaces the name of one thing with the name of something else closely associated with it."
Examples of this include the bottle for booze, the press for journalists, skirt for woman and Mozart for Mozart's music. The last one threw me until I realized that I listen to Tchaikovsky all the time, and no, he doesn't rise from the dead to play for me. This literary term is broad enough to include the names of places for their associations, such as Oval Office for the US presidency. And of course, this dictionary quotes a famous metonymic saying, the pen is mightier than the sword.
METONYMY VS. SYNECDOCHE
Now, according to this particular dictionary, Synecdoche is a kind of metonymy, which makes sense to me. It's defined as "the name of a part is substituted for the whole, or vice versa. An example is, I'll lend you a hand. No, you don't get to borrow my actual hand. But I'm available to help with a task, um, at hand. There are some purists out there who will argue that Synecdoche is not the same as Metonymy, because they feel that Metonymy should not contain a part of itself, but rather, it should be an outside entity that is related. I think they're splitting hairs. Really, it's more fun when you can brush those feelings aside.
Derek met Sally at the local steakhouse where she promptly ordered the house specialty, surf 'n turf. But the really big surprise was the diamond on her finger.
Surf 'n Turf = lobster & steak (Metonymy: lobsters come from the sea while cows live on land)
Diamond = engagement ring (Synecdoche: the diamond is part of the engagement ring)
METAPHOR VS. METONYMY
It's easier to see the difference between these two...
Metaphor invites a comparison between two unrelated things by pointing out some aspect that's similar, such as: He was nothing but a hound dog, sniffing all around (Thanks, Elvis).
Metonymy requires the two to be related, such as: They danced to Justin Bieber (his music, not him).
Metonymy serves up many a clever and creative opportunity. When writing about people, you might choose some intense characteristic they possess, and have fun at their expense. Let's pick on those who can't put down their phones ...
The night DrSteve linked up with Sheila7-11, it was a high-speed connection. He held his breath while sliding and tapping. She exhaled slowly while double-clicking. Each stared deeply, longingly, into the other's profile. It was as if a magical web embraced the lovers. Before long, they went from texting to sexting. Alas, he dropped the call when his iPhone XR 128GB Louis Vuitton declined a message from her profoundly incompatible Motorola Moto Android. "It just wasn't meant to be," he tweeted. "She had no plan."
The Candy Store Gangsters were quite the mix of brawn and brain. While three shifty third graders kept watch, fifth-grader "LeBrawn" Bruce made like a step stool for the brains of the operation, second-grader Lenny Snyder, who reached the sweets on the high shelf, flinging penny candy to his pals below.
And of course ...
The original Beauty and the Beast by Gabrielle-Suzanne Bardot de Villeneuve, plus all later incarnations, rely on Metonymy. In the Disney version, her true name is Belle (forget that it means "pretty" in French), and he would at least be referred to as the Prince (in any other story). Yet, the character's names are repeatedly replaced by descriptive notes.
PUT YOUR PEN TO PAD
So, go out there and try this for yourself. Sit in a public place and take notes about the people you see. Watch closely for some strong aspect or distinctive trait. What does his shirt say about his choices? What does her laugh say about her personality? What does it mean when such a small child shouts so loudly? Match that trait to a story or even just a plot point, and see what happens. Try it for Metonymy, Synecdoche (part of a whole or whole for a part) and even a Metaphor for practice. This exercise should help you recognize opportunities to work with associations, differences and messages that benefit from descriptions of both. Keep an eye out for fun!