Japan Photo #44 answer

To all who've been wondering what these triangular containers are, here is the answer. They are lunch boxes. Or to be more precise, they would each hold one triangular rice ball (onigiri).

So Karen in Cambodia came up with the closest answer:

I know sushi is a Japanese favourite, and I also know that the Koreans have a similar dish called Kimbap, which you can buy in the traditional roll shape or as triangles wrapped in seaweed. These would be the perfect containers for the triangle kimbap.

This is one of our favourite Japanese take-away foods.
It is a basic, something Japanese mums make like Australian
mums would make a sandwich.

Onigiri/rice balls are not sushi, but are made with lightly salted short-grained rice and usually have some kind of filling like fish or pickled plum and wrapped up in seaweed (which stops the rice sticking to your fingers). My favourite, probably not very traditional, is mayonnaise and tuna or salmon. These are readily available at convenience stores and are very portable. They taste best warmed slightly. We miss them when we're in Australia.