Umeboshi, or sour salted plums, are a staple in Japanese cuisine. The salty plum tastes great with plain rice, especially in an onigiri (rice ball)!
Japanese regularly make umeboshi tea by simply putting a umeboshi into green tea. Any green tea is fine, but sencha works best because of its simple taste. Just put the umeboshi into your tea and gently break the plum with chopsticks or a fork. The tea becomes salty, sour and a bit fruity. It tastes refreshing, and is a nice hangover cure!