What is the ruling on taking the money remaining from a lunch purchased with shared funds via a lottery?

If the money is shared between the two of you, then it is permissible for one of you to waive the remaining price of the food for his companion with his consent, based on the Almighty's saying: "O you who have believed, do not consume one another's wealth unjustly but only [in lawful] business by mutual consent." And the Prophet, peace and blessings be upon him, said: "The wealth of a Muslim is not lawful except with his willing consent." As for drawing lots to determine the winner of the entire amount, it is prohibited gambling.