ATMs are fairly common in most Southeast Asian cities. Outside of expenses like flights or hotels, I found it easiest to work mostly with
cash withdrawn from an ATM (for the best exchange rate). Keep only a portion of it with you at a given time and the rest in a safe at your hotel or guesthouse. Be sure to call your bank before the trip to let them know that you’ll be traveling, and where you’ll be going, otherwise they may mark international activity as suspicious and freeze your account.