Cash is king

Use monero or cash

If in the US, check out privacy.com. It's a bank so expect the signup process to be as invasive as any other bank, but they allow you to create masked cards and you can fill in any name and address you want into the billing info to keep your real info away from websites. Paid version also hides transactions you make from your actual bank.

Always carry extra cash everyday to pay at stores, never have debit/credit card in wallet unless it's to withdraw more cash, never give stores your number or name to buy or reurn something, do not give legitimate info to register for a free store card, never register for a tap pay service on cellphone, buy a pre-paid credit card if you can buy it anonymously with cash, for Americans, use privacy.com for card masking.

If you exclusively use physical cash with change at stores and never give a name, there's no behaviour prediction to get from you or how to advertise to you. Online purchases are not as good for data mining and tracking because there's no geo location like paying with a card at a store that can be used to track your movements and at what time you were there.

Additionally to what people have said, I have set up several banking accounts with different banks. That way, no bank has the full picture of what I earn or how much I spend.

If possible, i make online payments with Monero. For example hosting, vpn, anonaddy and a lot of giftcards.

Honestly nothing.

My problem is cash is really the only way to be truly private with your finances. Nothing else besides going great lengths using Crypto or gift cards is really private as far as I understand. I personally hate using cash, it is just such a hassle to use when compared to a debit/credit card. I always worry I don't have enough or I have too big of denominations, or I will fail at math and look like an idiot. It is annoying to carry around, if you live in a bad neighborhood it could be potentially dangerous to carry around.

I really wish there was a private mainstream finance option but I have yet to come across any.

Probably worth moving your e-commerce sites off your google, outlook etc. Proton mail would be good. I don't use open banking. Everything is debit card.