25Single Colored Currency
The US definitely has unique currency - and travelers are often confused when it comes to finding the right bill, because they are all the same size and color. In many other countries, different denominations are different shades (and even sizes), making it much simpler to pull the right bill
out of a wallet without having to peer at the numbers on it.
Other countries are also making the move (or have already switched) to dollar coins and plastic money that is longer-lasting and harder to copy, while phasing out of the penny. These are all things the US could definitely adopt.