All perfect praise be to Allah the Lord of the Worlds. May Allah`s peace and blessings be 

upon our Prophet Mohammad and upon all his family and companions.

According to its legal characterization/classification, school cafeteria is a partnership and Mudarabah where shareholders contribute capital, then appoint an agent to manage the affairs of the business. The Mudarib (working partner) is the agent that rabb-ul-mal ("silent partner", "financier") has consented to run the business, so he is trustworthy and must preserve the best interest of the authorizer (rabb-ul-mal ). The Prophet (Peace and blessings be upon him) said, "All of you are guardians and are responsible for your wards. The ruler is a guardian and the man is a guardian of his family; the lady is a guardian and is responsible for her husband's house and his offspring; and so all of you are guardians and are responsible for your wards." {Related by Bukhari}.

All the actions of the agent must observe the best interest of the authorizer to the fullest extent possible. Imam Shihab Ar-Ramli (May Allah have mercy on him) said: "A partner is like an agent in terms of running the business in the best interest of the authorizer." {Hasheyat Ar-Ramli Ala Asna Al-Matalib, Vol.2:P.257}. In addition, an agent is responsible for protecting goods against damage by adopting the best course of action to that end. Consequently, he is allowed to sell perishable products at a low price since this is allowed by the scholars. For more details, kindly check {Menhaj At-Talibin, P.174 by An-Nawawi}.

When the agent sells the surplus of perishable goods at a price lower than theactual cost, this lies in the best interest of the shareholders themselves as doing so preserves their wealth. However, if he couldn`t do so, then it is permissible to distribute this surplus amongst the shareholders (students), or give it to charity as this also preserves it against damage and waste, and is in favor of public interest. The Prophet (Peace and blessings be upon him) said, "Allah has forbidden you ( 1 ) to be undutiful to your mothers (2) to withhold (what you should give) or (3) demand (what you do not deserve), and (4) to bury your daughters alive. And Allah has disliked that (A) you talk too much about others ( B), ask too many questions (in religion), or (C) waste your property." {Related by Bukhari}.

It is incumbent upon the agent to fear Allah, be honest and give advice to his authorizer to be cleared from liability before Allah. And Allah the Almighty knows best.