What is the ruling on receiving monetary compensation for a service (lunch meal) from which employees still benefit?

If you know that you are not entitled to compensation, it is impermissible for you to take it unless the responsible authority permits you to do so after being informed. Otherwise, it is consuming wealth unjustly. The actions of your colleagues do not justify you doing the same; rather, you must accustom yourself to doing good, even if others do wrong.