This idea is from socalblue over at GBW. I think its worthy to be here as well.
The gist of the idea is to leave your car keys in your pocket. Bring an UNOPENED bottle of water into the stadium. Drink your water. Toss in change in the now empty bottle. Instant noise maker.
They seem to be gaining a decent amount of support for this and I thought it was a great idea. If you really like the idea and don't mind shelling out some water and change, bring extra water bottles and pennies to hand out at tailgates, etc.