noun
500-yen bento; one-coin bento
A boxed lunch sold for a single coin, typically a 500-yen coin. Common in convenience stores and supermarkets.
コンビニでワンコイン弁当を買った。
I bought a 500-yen bento at the convenience store.
最近、ワンコイン弁当の種類が増えている。
Recently, the variety of 500-yen bentos has been increasing.