On some luxury class cruises you can buy wonderful souvenirs and pay with your preferred Credit Card as major ones are accepted: MasterCard, Visa, Amex, among others; also you can pay for souvenirs at local shops in Puerto Ayora or San Cristobal with your Credit Card, but some of them will only accept cash payments. On board other category of cruises, payments must be done in cash (U.S. Dollars) for souvenirs and consumption.