What is the ruling on eating food purchased by a driver known for having many debts, and is it permissible to accept it if the source of his money is doubtful (from debts or from what is lawful)?

There is no objection to consuming what the aforementioned person buys if it is permissible and given willingly, even if the debtor is burdened with debts. The abundance of debts does not make his money forbidden to him, nor does it forbid others from accepting gifts from him. The basic principle is that what is in the possession of a Muslim is his property if he claims it. Ibn Taymiyyah said: "The basic principle regarding what is in the possession of a Muslim is that it is his property if he claims it." It is stated in Al-Majmou' by Al-Nawawi that "if lawful money is offered to him in a way that is permissible to take... it is permissible to take it without dislike."