Mix vinegar, sugar, and salt into the cooked rice to make sushi rice.
Spread the sushi rice evenly over the seaweed sheet.
Cut egg, cucumber, pickled radish, imitation crab, and spinach into long strips.
Cut the salmon into thick long strips.
Arrange all the prepared ingredients evenly on top of the sushi rice on the seaweed sheet.
Carefully roll it up so the shape holds together to complete the futomaki.
Slice into bite-sized pieces.