If you travel on a shinkansen do not forget to buy a bentō box called ekiben えべん in Japanese. You can purchase them on the shinkansen platforms close to the tracks or in the shops in the JR Japan Rail areas before accessing the tracks. It is part of the fun of traveling with the fast train. I always purchase an ekiben and something to drink.
There are a lot of varieties, so make sure to plan in some time for shopping before accessing the tracks. Some are served cold, some hot. These shops also carry a wide variety of sweets to purchase as omiyage おみやげ gifts to bring to family or friends or to each yourself of course.
Bentō box for dinner on the Shinkansen at around 350km. Nice!!