Upon entering the shack, turn left into the bedroom, the holotape will be on the bedside table. To access the safe deposit box, open the Pip-Boy, start playing the holodisk, and immediately exit the Pip-Boy 3000, before or after interacting with the voice-activated security system. The security system will report that access has been granted to the safe deposit box and it will open. The deposit box contains four stacks of pre-War money, and a sexy sleepwear.
...Don't tell Evelyn. The Password? "Buttercup", Why...
Even though the terminal in the bank says that Bern is male, the holotape has a female voice, the same voice that leads one through The Velvet Curtain.