FWIW, I use Fidesmo. Oversimplified, it allows you to copy your credit card's NFC chip into an accessory you wear. I use a ring but there are other options like bracelets or watch bands. No batteries, no devices, no wireless connectivity. It works anywhere an NFC card works, which here in Switzerland is more or less everywhere.
It requires that the card issuer support Fidesmo though. Many here do but I'm not sure what it's like elsewhere.
