I visited Belle vue recently and there is a full page in the programme of what is allowed at the meeting mostly to do with Health and safety but a slight overkill on no food or drink allowed in the stadium. This I presume even means water, so buy your water at the bar for £1.90 a bottle.
The stadium is a complete no smoking area including e cigarettes , which is nice.
Cannot see a ban on air horns but trumpets, vuvuzelas, flags, scooters, frisbees , flares skateboards, etc etc are not allowed.