Is it essential to have a toilet in a restaurant?

There are many situations that would influence this answer. First and foremost you must check with the Health Department that regulates your city and read their codes that will be the rules that must be followed. I have been to several restaurants in my days with no public restrooms but they were quick order and usually to go only with noeat in seating. If alcohol is served then you already know the answer, yes it's essential.