The types and amounts of coinage the PC's will find depends on the sources of such money in the campaign world. The currency can be newly minted, or produced thousands of years ago in some forgotten kingdom. It could be imported from overseas, made right next door, or the maker could be completely unknown. Trade with unknown or rare currency is difficult at best, and, if not kept simple, can make role-playing tedious. On the other hand, finding a stash of ancient gold coins that collectors want badly can be very satisfying.
Coins can be game clues, also.
Finding rare dwarven money in a dead bandit's pouch can mean someone has discovered an ancient dwarven hold in the area. Finding money can be much more interesting than counting gold and silver pieces. Beautiful jewelry and gems are some of the most sought after nonmagical items that characters may find. Portable and extremely valuable, characters finding them can turn a great profit with little trouble. The amount that PC's will get from gem buyers can vary greatly with the buyer's honesty, also.