Depending on the place you're going to, keep in mind that the currency may be different. As such, the official currency in Spain, France, Italy, Portugal, Germany, Austria, the Netherlands and most other EU countries is Euro. Rubles are used in Russia, Norwegian Krones in Norway, Swedish krona in Sweden, Danish krone in Denmark, Hungarian Forints in Hungary, Czech koruna in the Czech Republic and Polish zloty in Poland.
It is best to have your debit and credit cards with you during your trip as many places including restaurants and hotels accept them. Plus cash can be easily withdrawn in ATMs, but note that you may be charged a fee by the bank for currency conversion. We also advise having some cash with you so you for pocket expenses.