I agree with most of your points.
I think that the rental car company should have given a list to the customer and they should have shown the supplies (I do not assume that they didnīt). The company should be able to offer explanations. I consider this reasonable service.
But from that point on the person is reponsible for himself. There should be no need for new regulations.
Does anybody really believe that these warnings do any good?
Actually they are good for a laugh and a who-finds-the-dumbest-warning contest. My favorite is "warning sharp blade" on a knife.