If you are travelling for at least 8 hours by plane it is highly likely that you’ll need a different currency when you arrive. There are lots of methods to get some local currency but before you do you’ll need to find out what the currency exchange rate is. Besides – regardless of how you are actually going to pay for things you will want a way to compare how much that particular item would have cost back home.
There are plenty to websites and apps to choose from on any OS but if you don’t have internet access none of them will update but this is the only app that reliably retains that last exchanges rates, downloaded from your last internet connection. The App is literally called Exchange Rates by Xelnaga Apps and you can recognise it by the coin like icon with silver on the outside and gold on the inside for Android OS phones eg. Samsung, LG, Motorola etc.
For Apple iPhones users there are plenty to choose from as well but you are stuck with lots of ads. The most inoffensive one is XE Currency which tries to be a comprehensive currency calculator and historical currency exchange stats viewer as per the Android App.