I use my password manager for those. The only card I have in my Apple wallet is my grocery card. Otherwise, I go to my password manager and pull up the entry and the attached images. Some, I have just a barcode png. Others I have screenshots of the card from an app/website. This has been a really good balance for me.

As an aside, I tried to use base64 for the images so everything was in text, but decoding with a shortcut was annoying enough I went with the image attachment.