>>279869703
It is usually frowned upon to bring tupperware to a buffet. The Japanese term here was "タッパー" which is "tappaa" so clearly a loanword from the brand name.

Also, googling a bit, it seems Japanese people don't do "to-go" boxes for leftovers in general at restaurants.

And yes, the sign said "Sweet & cake" with English letters in the Japanese original as well.