Bank accounts and brokerage accounts in the US can be designated to be Payable on Death (POD) or Transfer on Death (TOD). This is legal in almost every state. The funds will transfer to the designated beneficiaries upon proof of death. POD/TOD takes precedence over a will and does not have to go through probate.
I assume that if a will contradicts the POD/TOD designated beneficiaries it would open a can of worms though. When I had my will made the lawyer made no mention of bank or brokerage accounts to avoid any conflict. Same with Thai assets, no mention in my US will and was advised to make a separate will in Thailand for Thai assets.
I think this has been brought up before and is not available in Thailand unfortunately