iCloud Keychain is a really good place to store your credit card information. It's encypted, easy to use and it syncs automatically between all your Apple devices.
This is how you add credit card information to your iCloud Keychain:
- Go to Settings > Safari > AutoFill > Saved Credit Cards and tap Add Credit Cards.
- Tap Use Camera to photograph and extract the credit card information automatically. You can also add the information by hand if you prefer that.
Next time you need the card information you can find it in the same place. You can also have it automatically filled out in web forms in Safari.sc