Both. Some places it is just easier to pay cash. Plus you shouldn't use debit cards when paying for gas. Gas pumps can have "skimmers" on them where crooks get your data when you swipe your card and can deplete your account fast. You don't need that hassle when traveling. Credit cards are safest at the pumps if you pay them off every month.
i would take both because if you only take a card and you lose it............but if you take cash,depending on how long your staying and how much you take you could run out, but if you take both you can use an atm to get cash. and also use the card.