The calories of box lunch are relatively high, because the ingredients of box lunch include rice and various dishes, so it is impossible to accurately estimate how many calories there are. If there are more vegetables, the calories will be relatively low, but the meat dishes will be rich, and the calories will increase accordingly.
Precautions for box lunch:
It is best to have a refrigerator (cold storage) and a microwave oven (heating) in the office. If you don't have both, you have to use that kind of lunch box with very good insulation, pack hot meals in the morning, and there will be residual temperature at noon. Because of its good sealing, it generally does not sour and deteriorate. However, as a suggestion, if you want to be foolproof, you'd better put your own box lunch in the refrigerator and heat it before eating.