I found some tiny little "rubber" bands at the local dollar store, meant for girls to tie their hair into pony tails. They're not really rubber, but instead some sort of stretchy plastic or vinyl that can be stretched to incredible lengths before breaking. They come in all kinds of different colors, and I bought a package of 500 black bands for (you guessed it!)............ a dollar.
Picture courtesy of Ebay in the UK. The bands I have are only about one half inch in diameter. Wrap 'em twice around the coupler, and you're good to go.