Depending on the type of "exchange" you're referring to, the most "useful piece" can range from a historical coin to a versatile travel tool.
: A versatile piece that most people can use daily. exchange
Is this related to a (like chess) or a historical topic? Depending on the type of "exchange" you're referring
: Frequently cited as a surprisingly useful and appreciated small gift. exchange
Historically, the most significant "piece" for exchange was the , famously known as a piece of eight . It was a silver coin worth eight Spanish reales and was widely used as the first international currency because of its uniform standard. Useful Pieces for a Student or Travel Exchange
: An invaluable piece for exchange students facing cold winter months abroad.