I've had this trick in my repertoire for years because it's portable and impromptu. I coincidentally wound up with two of them which turned out perfect for enhancing the effect. When I decide to perform this, I discreetly place one of the other coin pieces from my back up into my mouth which can be loaded there while conversing and even eating and drinking if you're careful. When ready to perform, after the bite is taken out of the coin, I can produce this extra piece on my tongue for displaying to the spectator which totally convinces them you have indeed taken a bite out of the coin.
When restoring the coin, just park the extra piece back under your tongue and "dispose" it later when convenient.
As an aside, replacement bands can easily be obtained at your friendly orthodontist at probably no cost to you. Over time, they will wear out or break. Hope these ideas help

One of the best impromptu tricks out there, good product that should last me a long long time. People would be in shock and awe whenever I perform it, well most of them cause the trick is revealed in youtube.

learn the palm switch and ask the spectator for a quarter..if you buy 2 you can actually show the piece in your mouth before you blow it back together, also great for winning money from drunk people at bars (I bet I can fit a quarter into the top of my beer bottle) keep the beer full so they cant inspect it with out messing up your beer