Back when I first traveled abroad it typically was not a big deal. After all, it was Canada. While the currency was different it was still dollars and dimes and pennies. Depending on the exchange rate at the time, it might be good for Americans or it might be good for Canadians.
Reaching across the big pond a couple of decades ago, I figured to use American Express Travelers Cheques. It meant for example that you had to find someone to cash it and if no one would do it, you had to go to the bank. You know about Bankers' hours. I guess they were protected, but it was certainly hard to cash sometimes.
Next came credit cards. The challenge here was whether or not the vendor's credit account was in the same network. Look at the back of the card to see what I mean. This is not the bank that issues the card, but the international network they communicate in. Think NYCE or STAR or Cirrus for examples.
Debit cards started being used in the States about 50 years ago but not widely used until the 90s. When my credit card did not work in Paris (the network issue) I broke out the ATM, slide into the machine and bought tickets for the elevator in the Eiffel Tower.
I found out later that I needed to know the PIN for the credit card, something I never used in the US.
Today, the US caught up with the rest of the world and added the chip in our plastic. A PIN is needed and it will probably work anywhere. The network issue should not be a problem, but I always call my credit card company before travelling and let them know what countries I may be visiting. I also let me debit card bank know, since it was a pain to have to call the bank from Iceland so I could use the ATM!
Lastly, I do try to have some cash on hand, maybe equivalent to $US 20 at least. In some places that doesn't buy much, but in others you can feed a family of four at a decent restaurant. Since plastic is basically used everywhere, cash is becoming less important. But I have yet to buy a cup of coffee with plastic (except my cell phone app from Starbucks).