Set it up
Install ShowCards on your phone and the watch app comes with it, from the Watch app on Apple Watch, or alongside the phone app on Wear OS. Once the two are paired, your cards appear on the watch automatically.
How it works
Your phone does the work: it renders each barcode and sends the finished image to the watch, so the watch never holds your card numbers or any keys. Nothing sensitive is stored on your wrist, and your cards stay available even when your phone is not to hand.
Put a card on your watch face
Add the ShowCards complication to your watch face and your top card sits right there, one tap away. It is a shortcut, not a scannable barcode: tapping it opens the card in the watch app, ready for the scanner. On Apple Watch, edit your face and choose ShowCards in a complication slot; on Wear OS, add it from your watch face's complication settings.
At the till
Open ShowCards on the watch, tap the card you need and hold your wrist under the scanner. If a small watch screen is awkward for the cashier's scanner, your phone is always the reliable fallback.