Bento really isn't designed to be eaten while driving (or even moving around). Eating while standing would be possible but probably less than ideal. Most bentos are designed to be eaten with chopsticks.
The primary on-the-go food would be onigiri, with "festival booth" foods second (mostly stuff on a stick e.g. karaage, dango, yakitori, takoyaki, ikayaki).
The primary on-the-go food would be onigiri, with "festival booth" foods second (mostly stuff on a stick e.g. karaage, dango, yakitori, takoyaki, ikayaki).