Do the food vendors come around when you are watching the game, or do you have to get up out of your seat to get food? I am curious because even in America I hate getting up for food durring a game, id rather just have someone bring it to me so I dont miss anything.
You can also buy food from the people whom are selling it in the stadium, they are walking around with beer, drinks, Yaki soba, etc. Negative thing is: it's expensive.
So my advice is, as Pipokun have said: Buy your food before the game.
Do the Japanese Stadiums have lists online somewhere that show what food vendors they have? I know in America you can look to see all the different places selling what foods.
Snacks like popcorn, chips, burgers and drinks like coke and beer are the same.
The most different food might be the boxed lunch, bento. Bento boxes at Yokohama Stadium
Or the Tokyo Dome Stadium sells the mouse, duck and cat. Tokyo Dome