Have you ever been to a Japanese restaurant for a meal and you could not finish your food?
Do you know that some Japanese restaurants would allow you to take leftovers home?
You can ask the waiter o waitress about the possibility to take leftovers home.
Use the following phrases to communicate with the waiter or waitress,
Sumimasen, nokotta tabemono wo omochikaeri ni dekimasuka?
Excuse me, can I box this up for me?
Please remember, some restaurants would refuse to let diners take their leftovers home.
Hope this helps!
Enjoy your stay in Japan!