However you travel, be it by land, sea or air, you need money. More money than you would probably need for the same amount of time at home following your daily life. There is always the unexpected to deal with — The Emergency Fund — and money to pay to get around, pay for hotels, and such.
Here are some of my observations after my latest foray into foreign territory where the European-wide cash card/debit card I carry was fed into the wrong slot of a ticket vending machine and promptly swallowed up along with all my Euros.
A lot of people advise credit cards for travel. This is usually because the conversion rates can be more favorable. There are, however, transaction fees on many cards as well as the exchange conversion rate. Some cards do not charge for transactions in the same currency which makes traveling around Europe a lot cheaper if you are European. Credit cards are also favored because, even with the charges incurred, they cost less to use than old fashioned travelers cheques.