The person who makes the bento, such as the mother of the household, often prepares the box lunches as she is cooking the side dishes for the family's regular meals. She considers which dishes would not go bad so quickly and sets a portion of these aside for the following day's bento. Indeed, the mother often plans the family dinner around items that will make good leftovers for the next day's bento.
Japanese people attach great importance to the appearance of their food. Part of the fun of making a box lunch is creating a visually appealing arrangement that will whet the appetite.
info credit: http://web-japan.org/kidsweb/virtual/bento/bento01.html
Bento - Wikipedia, the free encyclopedia
... child, or themselves producing a carefully prepared lunch box. Shōkadō bentō (松花堂弁当) is a traditional black-lacquered Japanese bento box.
Japanese Box Lunches - Virtual Culture - Kids Web Japan - Web Japan
Box lunches (bento) are very popular among Japanese kids and adults alike. People take them to work, to school, on picnics, and so on.