Must a partner in a grocery store pay for his food and drink consumed from the store, and is he required to ask his partner's permission to allow an employee to eat and drink from the store?

It is not permissible to eat from common money or allow an employee to do so without the partner's permission. However, if custom dictates allowing a small amount of food and drink, and the partner's consent to this is known, then there is no harm in eating and allowing the employee to do so within the bounds of custom, because permission is obtained by custom even if it is not explicitly stated. But if the custom is disrupted or there is doubt about the partner's consent, then it is not permissible except with their explicit permission.