I am using a Notes app to keep track of all Cards, Bank account details, all email and app passwords and I keep it hidden from the app list. No one can find it even on an unlocked phone except me.
Also I keep the transaction limits to bare minimum and always turn off International and ATM transactions for all cards, disable Tap n pay for those which I don't use.
Also I have learnt not to save card details in websites and apps except for a few trusted ones. I use Flipkart every month but none of my cards are saved there whereas in Amazon, Paytm etc all cards are saved.