Musubi

Cooked sushi rice (still hot/warm)
ume pickle (or some other salty pickle)
Salt
water
Nori (dried seaweed sheets)

Cover your hands in water, then salt. Then shape a handful of rice into a triangle shape with both hands. Poke a hole into the middle and insert the ume (deseeded). Then cut a strip of Nori and wrap it around both sides. Eat immediately or wrap in plastic wrap. Don't refrigerate, but it should last a couple of days at room temp.