Is it permissible to give employees extra quantities of food and drink, at their request or the manager's request, as long as they consume it on-site and do not take it to their homes, with the manager's knowledge and approval, and as long as the basic quantities are available?

The determining factor in what is disbursed to employees is the labor regulations and systems, and what is decided by the authorized person. If the manager is authorized and permits a larger amount to be disbursed to employees, then there is no objection. Otherwise, it is obligatory to adhere to what the regulations require, which is that each worker be given only what is allocated to him.