You can have 2 Thai bank accounts. I put the one for the immigration funds separate, it’s not accessible by ATM, though I can transfer to/from it online. It draws interest. I never touch it except to update the bankbook. I keep a little more than the minimum. Remember you must update the book and get a letter from the bank when you extend your stay, so time deposits, banks not at/near your immigration office–are problematical.
If you are on a Non-O retirement visa, be aware of that, as far as I know, in addition to testing, special flight, covered insurance, and quarantine, you must have general medical insurance for 400,000 baht impatient and 40,000 baht outpatient. It can be quite expensive and provides very little coverage. Hopefully that requirement will quietly disappear in a few months.
I did that, on third renewal. They started requiring Thai health insurance to renew OA, before Covid. Not on O retirement extension. But I hear they are requiring medical insurance for NonO’d on reentry permits
It’s not that, we are afraid of losing it or getting it mutilated such by as I getting moisture from rain or sweat. I carry a copy and thai drivers license. People have been taken to the police station until their girlfriend could go get their passport and bring it. But I figured that would be less hassle than losing a Passport with visas, etc. in it.