What is the ruling on eating and drinking from what students bring to school?

There is no objection to eating food brought by students or others at celebrations and occasions if the person is invited, or if it is customary to do so, or if it is known that those who brought the food are pleased for all attendees to eat from it. However, if one is not invited, or if it is known that those who brought the food are not pleased for others to eat from it, then it is not permissible for him to eat, due to the Prophet, peace and blessings be upon him, saying: "The wealth of a Muslim person is not lawful except with his good will."