Possible Clues:

• Soft-drink freebie, sometimes
• Top up glass, replenish
• The referee being indisposed, this seems to be the substitute
• The referee being sick, this is a stand-in
• Second glassful
• The referee, being indisposed, can be only a stand-in
• Top up glass or petrol tank
• Well, the referee isn't a substitute
• Take rifle out to lake for another shot
• Common ink purchase