There are many good answers already, and having had my troubles with cards throughout Europe, let me try to put forth another answer.
You mentioned you are from South Korea, so I assume your bank is also based there.
More often than not, paying with a credit card incurs some extra fees that debit cards do not. Check with your bank if that's the case. I have yet to see a super market that didn't have contactless payments in the past few years, so I think your debit card is fine. However, many vending machines and ticket machines sometimes require you to insert the physical card, so Samsung/Apple Pay might not be an option there.
However, with a credit card, it's bank's money that you use first, and comes with better protection against stolen/skimmed cards. I personally never had any problems, but a friend of mine had some money taken from her card. We were in Germany, and the charge was made in Bosnia, and it was easy to inform the bank and reverse the charge a few weeks later.
Car rentals, in-flight purchases, etc. often require a credit card, and I highly doubt Samasung/Apple pay can help anyone there.
Contactless payments also often have a lower limit. Sometimes it requires the card holder to enter the PIN, or sometimes to downright insert the physical card.
With all that said, I think your best option would be to obtain a physical debit card, a credit card, and setup your phone with both of them. This way, you can have all the backups you need. Pay with your phone when it works, with debit cards otherwise, and use the credit card if you were to rent a car. If the credit card company does not charge a fee for foreign transactions, use the credit card whenever you can.