Apple Card is widely accepted and has no foreign transaction fee. In addition to that, there is 2% cash back when using Apple Pay with the Apple Card.

Another card good to have on hand when there isn't Apply Pay is Amazon Card which also has no foreign transaction fee.

For cash situations like additional tipping (which is not very common in Europe by the way, which is why they won't have a receipt line for it when using credit card like they do in USA) or like using small services like the bathroom (some require coins) or street food, then we recommend doing a few hundred exchanged before you travel to have on hand. Just look at reputable currency exchange places on Yelp, you can likely find one that doesn't charge much of a fee if any and just check against current exchange rates. If you're in Southern California, we can recommend Continental Currency Services located in Santa Ana.