Although Japanese food is known for its fresh fish, it’s easy to make vegan sushi. Sushi and onigiri are treated as snack food in Japan. I think they are the perfect plane food. (If you are travelling, another option is to order the Asian meal, which is usually vegan and pretty good.)
It is fiddly making sushi, but keep practising. I had a Japanese cookery lesson with Hiromi Stone and she emphasised the importance of fresh ‘new season’ rice, so check the dates on the packet! She prefers Californian sushi rice rather than Italian, as it is better quality. Authentic Japanese sushi rice is quite expensive.