Credit/Debit cards are widely used, however you may still need cash for small things like tipping or paying for taxis or buses. Most credit card companies in the US impose a foreign transaction fee on items and services purchased outside the US. Be sure to get in touch with your credit card provider before you travel.
Be careful of your money, wallet, and credit cards when you are in crowded areas like markets, buses, metro stations, subway cars and train stations. Your pocket could be picked at these places if you’re not vigilant.