I buy chicken/beef bouillon powder and use that with dry noodles. You can make a mushroom broth by steeping dried mushrooms in hot water for 15-30 minutes, too.
Someone else mentioned daishi, that’s a great soup base as well. If you wanna spend a little more time on it, you can boil kombu and dried anchovies placed in a tea bag in a pot of water to make a larger batch of broth.