Coins were a type of currency found within the galaxy. While the standard of the Galactic Republic was credits, some merchants, particularly from Outer Rim planets like Tatooine, were wary of their value. They preferred funds that were less likely to fluctuate in value if a government were to crumble. Watto, one such merchant, advertised all prices at his shop in coins.
Anakin Skywalker flipped a coin to determine whether to remain with the Jedi Order or change sides and join Darth Sidious and the dark side of the Force. The coin flip determined that he would join the dark side.