What is the ruling on a small quantity of provisions designated for the poor falling unintentionally during distribution, and is the donor obligated to cover the cost of what fell if the person in charge prevented him from touching it?

It is not permissible to be complacent in safeguarding trusts. Whoever falls short and is negligent in safeguarding what they have been entrusted with is liable for it. However, if negligence occurred without dereliction of duty, then there is no liability.

If the negligence came from an official, then he is only liable for what he was negligent in safeguarding. He should strive to estimate what was damaged and is only liable for the damaged portion, not the entire bag.

The jurisprudential rule is that fungible items are guaranteed by their like, and non-fungible items are guaranteed by their value.