Umami, the "fifth taste", can be added to dishes with lots of ingredients, but few deliver the bang for the buck that kombu does. It's affordable, easy to use and packs a big savoury punch in soups, stews, sauces or just dried and sprinkled over food. Image from joyosity.
You can find kombu at your local Asian grocery store or online (like this pack from Fountain Of Being), and if you're lucky, in the Asian section of your supermarket. Each pack contains multiple strips of kombu, and if you're making soup, stew or a broth, you'll only need to use a small piece of kombu in a batch. If you want to get the most flavour out of kombu, soak it in water overnight before adding the rest of your wet ingredients. Overall, it's a very inexpensive ingredient. Store it in an airtight container away from sunlight and moisture, and you'll have an umami bomb to add to just about any dish.
Ingredient Spotlight: Dried Kombu [The Kitchn]