In the cartoon below there is a man selling ice-cream, and a...

In the cartoon below there is a man selling ice-cream, and a sign on his stand that says “The end is near, have a cone”. The word “cone” is countable, and that is why it was preceded by an indefinite article. What would be the correct form if we added “ice-cream” before “cone”?

Source: @newyorkercartoons