Converting unused dollars: Ideas for Social Innovation

Every day there are thousands of public transport travellers in cities across the world who have unused fares in their travel cards or equivalent tickets.
Is there a way to monetise these unused small currencies and use it for a noble cause ?
Recently I came across this article where few students from New York university have designed a system which can be used to convert unused dollars for social causes.

MetroChange has designed a kiosk to be placed at busy subway stations throughout the NY city — “especially those where tourists and occasional users of the subway transition out of the subway system, transferring to an airport or regional train service”. Commuters and travelers who have a small amount of unused value remaining on a card can swipe that card at one of those kiosks, where the value will be recorded and transmitted to a central fund .

MetroChange from Genevieve Hoffman on Vimeo.

For me this is a brilliant idea which could be shaped up from this basic level to several interesting applications .
My ideas on we could use this in other areas:

Sure, lot more could be achieved with things we waste !