After last weeks compass tip I was asked if that was the cheapest bit of kit in my camera bag? The answer to that is no as the cheapest thing in my camera bag is a rubber band!
I carry this as sometimes when unscrewing a round filter or an adaptor ring for Lee filters they become stuck on the lens and can be a pain to remove, particularly when you want to be quick when light is changing fast and your fingers are cold. When this does happen the rubber band gives a good grip making it easy to remove the filter or adaptor ring.
At a cost of under a penny you can even splash out and carry a spare, but hopefully not have to use it too often! You could also follow your postman as he usually leaves a trail of them saving you money!
Whats the cheapest accessory in your camera bag?