If you need formal clothes while travelling, you might feel like you've got two options: lug a separate garment bag, or use an iron when you arrive. This video shows how to fold your jacket for a suitcase without surrendering to wrinkles.
You'll probably have to watch it once or twice to get the folds down, and maybe keep your laptop open while you follow along. But when completed, this fold gives you a squared-away jacket/coat that you can presumably slip on when you're ready to roll into your job interview, wedding, funeral, or whatever you're heading out for.
There are alternatives, like the bundled packing method and straight-up rolling, but the shape (and cost) of a coat makes it less adaptable to alternative methods. Unless you've found otherwise—and tell us so, in the comments.