If you have used the iCloud Keychain for storing bank card information, you have probably noticed that there is no field for storing the security codes (Often called CVC/CVV/CVD/CSC codes). Would you trust the security of iOS and iPadOS to store this information? Then I have a trick for you.
Credit card information is stored in Settings > Safari > AutoFill > Saved Credit Cards. The Cardholder, Number and Expires fields are used for auto-filling credit card information in Safari, so you can’t change them, but the Description field is for your personal description of each card. Write the security code somewhere in that field. Then, whenever you pick a card to use with AutoFill, you will see the code to enter in the proper field.
Make sure to secure the sensitive information in your iPad with a good password. Otherwise, using it for storing sensitive data is a bad idea.