What documents do I need for a retirement visa renewal at Chaeng Wattana using bank funds?

You need three things if you are using banked money method for proof of funds on a retirement extension

Standard bank letter <- this just is a few lines says your name, passport number, account number and balance the date the letter was written

Year detail transaction report <- if you are getting a new yearly extension from a year extension you need the year detail transaction report so that the immigration officer can see that you followed the post extension seasoning last year when your extension was granted (meaning you kept the 800K funds in the account for 3 months and then never let the balance go below 400K the rest of the year)

These two documents can be up to 7 days old, so no issue getting them ordered, printed before you slog out to Chaengwattana.

Dunno if you can order them for pick up at C/W branch or not, but seeing as you can have them up to a week old it doesn't matter, just get them a few days before you go for your extension

And you need to update your bank book the date you apply for the extension to show the current balance. That usually entails doing a small withdrawal or deposit the day of your application to make the passbook update machine print a transaction detail for that date.