What is the ruling on eating hospital food brought by a cousin without permission?

It is not permissible to take food designated for patients in the hospital except with the permission of the owners or the authorized party, because it is consuming wealth unlawfully. If your relative takes food without permission, then it is not permissible for you to eat from it, and you must advise him and forbid him from this evil, unless the food exceeds the patients' needs and the hospital owners wish to dispose of it, in which case there is no harm in benefiting from it.