A somewhat relevant scenario:
Back when I was throwing my house parties, it was widely known that for everyone's safety, all car keys were to be put in a certain box, which in turn was locked securely away. Only I had the key to that. If a person had driven there and was going to imbibe any alcohol, they were there until at least the following morning. Period, full stop, end of story. Use this as an example of an implied contract.
This was done to protect against the possibility of anyone from my place driving under the influence. Therefore, it was done in everyone's "best interest". Sure a couple of people complained, and they were told that if they didn't like it, they didn't have to be there (unless they were already drinking), or simply stay sober the entire time. In the several years I threw those parties only one person broke that rule (they had a second set of keys I didn't know about until it was too late), and the parties happened every weekend.
One caveat: The cars were not parked on private property, so I could not prevent people from going to their cars if they wanted to. They also did not have to provide ID and registration before leaving, as I already knew who was who and who drove what.