Possible Clues:

• Food-freezing agent
• New cider includes the last of the scrumpy - it's provides a special effect
• Stage mist
• Fog machine substance
• Last two characters in 14 across consumed by betting object found in special effects kit
• Haunted-house supply
• Smoke on stage, taking gamble about lines
• I decry the making of gas for stage effect
• Source of theatrical effect – risk bringing in railway
• Doctor with ponytail I see gets direction in dramatic mist