Leonard has a Motorola Moto G7 with a 5,000 mAh battery. Leo says that'll last forever. But the G7 doesn't have NFC, and he needs that. Leo says you can't add NFC to the phone, but you could get an Android Wear Watch that supports NFC and you could pay for it that way. That would be the easy way. You just have to be sure the model you like supports Google Pay. The Wyze Band fitness watch supports Google Pay and it's only $25. Fossil makes several, as does Casio. The Fitbit Charge 4 as well.
Or just upgrade your Moto to a new model that supports NFC.
From the chatroom: you can also talk to your bank to get an NFC key fob that would do it. Lastly, you could get a credit card with NFC, and it would work the same way. But that won't be encrypted.