I assume that most of the non-Japanese think sushi contains raw fish or seafood. However, it is not true.
Actually sushi does not have any meaning of raw fish or seafood but it must contain rice with sweetened vinegar. Rice without rice vinegar and sugar are not considered as sushi. Therefore almost anything with rice containing rice vinegar and sugar can be called sushi.
Most common sushi eaten outside of Japan is nigiri sushi or maki sushi. Nigiri sushi contains raw seafood and maki sushi contains seaweed. Nigiri sushi and maki sushi are provided at sushi bars, sushi restaurants and supermarket or sushi specialized take away stores.
Convenience stores which are opened 24 hours hardly offer nigiri sushi due to its freshness. Nigiri sushi must be made at the place where you sell the sushi, not at the factory far away located. Thererfore the consumption of nigiri sushi is not so high as you expect before going to Japan.
There is a sushi called inari sushi. The rice is wrapped with deep fried tofu called abura-age. The aburaage used for inari sushi is stewed with soy sauce and sugar and cooled down before wrapping the rice. The rice can contain just sesame or other ingredients such as chopped and stewed vegetables and mushrooms.
Inari sushi is also offered at convenience stores and diners which is not specialized in sushi. It is very worth to try it and also suitable to take away and eat inside the train.
By the way, inari sushi is also called oinari-san or oinari. Inari is actually is one of the Japanese kami(god) of foxes. It is legendary told that foxes love abura-age and therefore this sushi is called inari sushi.