cash or credit card

Bring at least one credit card. And bring a debit card to get cash from ATMs once in Greece. Make sure you notify the CC companies and your bank in advance of both your dates and which countries you will be visiting.

I use both credit cards for big charges and local cash from ATM withdraws after arrival for small purchases. My travel Visa credit card is a Capital One and my travel ATM is a local credit union that charges a 1% FX fee.

RS FAQ tips:
https://www.ricksteves.com/travel-tips/money/card-fees

Capital One has a particularly good reputation for no-fee
international transactions on both its credit cards and its debit
cards linked to a checking account. Most credit unions have low-to-no
international transaction fees. Bankrate has a good comparison chart
of major credit cards and their currency-conversion fees.

https://www.ricksteves.com/travel-tips/money/cash-tips

Resist the urge to buy foreign currency before your trip. Some
tourists feel like they just have to have euros or British pounds in
their pockets when they step off the airplane, but they pay the price
in bad stateside exchange rates. Wait until you arrive to withdraw
money. I've yet to see a European airport that didn't have plenty of
ATMs.

Just a note about Capitol One, or any other credit card from a Canadian institution. There's no such thing as a no FEX fee card in Canada. They all come with a built in add on that will amount to 2.5% over the current exchange rate. Canadian bank cards (ATM or debit) will all charge an extra transaction fee of up to $5CDN per transaction. Unlike some American cards that charge no or low fees.

I need to modify my previous post. It seems there are 3 CCs that will cover the forex fee: 1) Home Trust Preferred Visa; 2) Rogers Platinum MasterCard; 3) Fido MasterCard.
I just found these on another site.

Excellent answers about strategic choices of Credit cards and ATM (Cash cards) -- I've copied for cut-and-paste answers to this VERY frequently asked question. One thing should be added, for US inquirers ... Credit Union ATM cards are marvelous because they do not have a 2-3-4% fee for withdrawals (the 1% Clearinghouse fee is built into the exchange rate). In US formerly you had to have a particular employer or be a state worker to have a credit Union account, but now in many states, such as mine (PA), you can get one by simply being a resident. However -- you can't open an account, get a card, and arrange to use it overseas all in one week, as u can with other institutions, so u must think ahead.

I'm going in June from Canada. I've read to bring cash which makes me nervous but I understand it can be necessary. My PC bank card doesn't work everywhere in Europe, as I found out when I went to Italy. I have to use bank machines with certain logos on them, mostly around places that you can exchange money. I will check again with my bank before I go. I ordered a Rogers credit Card that doesn't charge the international fee of 2.5% on transactions. I got a year without the annual fee.

MY PC card has worked fine in Italy on several trips (both credit and ATM debit.) I always carry a set of VISA-related cards too, increasing the chances of one or the other working -- but the rejections have been rare on either system. (That's President's Choice, a large grocery story chain branding a MasterCard -- not PC as in politically correct.)

I have never had any problem using my Scotiabank Visa and debit cards in Greece at any ATM’s. I do always get some Euros before I leave home, €50 or €100, so I have something on hand for immediate use so I am not looking for an ATM straight off the plane or as soon as I get to my hotel. Just make sure you call the number on the back of the credit card to let them know you will be using the card in Greece.

All great info!

Both cash & CC are needed.
Capital One is great with no foreign tranaction fees.
We never had an issue with using it in Europe.
Do NOT use AMEX in Greece. Took it with me (habit from US home). Bad.
Do NOT exchange money prior to entering Greece.
Lots of ATMs in airport. Ue them.