Well, Nepalese rupees are the best acceptable currency you can use on the trek. It becomes easier for the shopowners and the hotel owners to do calculations if you pay in rupees. You can still pay in your own currency but it is not a suggested way. You have to check out the exchange rate every day which is a very tedious job. It is so boring to even think about paying in the foreign currency according to the exchange rate daily. It becomes easier for you to plan your expenses if you don’t have to think about exchanging.