Lawson, you're showing your age posting this, and I'm showing mine by responding. I'll bet they haven't bottled a fifth of liquor in this country for fifty years. I will admit it's awkward to say "Be prepared for the 4th, get 750 millilitres on the third. Don't be caught short."
That just don't work at all.
For all of you young whippersnappers out there, it was called a "fifth" because it was a fifth of a gallon. Why? I don't know; it may have been due to some arcane way they taxied liquor back in those days.