Contactless payments via phone would only be possible if you had a banking app that provided the feature independently. Google Wallet/Google Pay does not work on OSes not certified by Google.
My main use of Google Wallet is to pay for the bus where I live, but we do have physical cards that I can also get. I do use it at the store sometimes but I also always have my physical wallet on me, so that's not a big deal.
Curve Pay also works, as do European banks using the standard approach not dependent on Google Play. Tap-to-pay is not an issue for GrapheneOS users in the UK and EU.
