Money is absolutely essential for traveling. The thought of being in a foreign country and running out of money -- or having plenty of money but not being able to access it -- is terrifying.
This article from the New York Times details some credit and debit card related horror stories from users who traveled abroad. I have been a victim of this - my card was denied in Ireland due to a glitch in the fraud alert system, and I was stuck borrowing money from friends until I got back to England and could call my bank. It was, in a word, TERRIBLE. Another word: FRIGHTENING. Yet another word: RIDICULOUS.
If you're considering an international trip, read the article and be prepared! Accessing your money is as important as budgeting it. Word.