No unmixed spirits shall be sold or offered for sale at retail for consumption on the premises, except in a container having a minimum capacity of at least one fluid ounce and which contains at the time of sale at least one fluid ounce of the beverage being sold. The provisions of this Section shall not prohibit the sale of unmixed spirits on boats or railroad cars licensed to sell liquor for consumption on the premises in containers regularly used and having a smaller fluid capacity.
235 ILCS 5/6-26