Is it permissible for a well-off person to benefit from non-monetary charities, such as drinking from water coolers designated as charity, or eating dates given as charity at iftars in the Grand Mosque of Mecca?

The sadaqa that is not permissible for the rich is zakat. As for voluntary sadaqa (sadaqat al-tatawwu') it is permissible for both the rich and the poor, as it is considered like a gift. However, it is preferable for the rich to refrain from it and practice self-restraint. There is no harm for a rich person to drink from water coolers or eat from iftar dates if it is a general sadaqa. But if it is specifically designated for the poor and he is aware of that, then he should not approach it.