Incompetent script (spoilers)
The scriptwriter didn't seem to have any idea how to create a dramatic or risky situation other than making the good characters act like complete idiots.
It would have been bad enough for a spy to leave all that incriminating stuff spread out in plain view in his cabin - with the door left open, yet! - if he had been forced to rush away by a sudden emergency; but surely no secret service would employ an agent who would just not bother to put it away, let alone lock the door, whenever he went ashore.
Similarly, the way the Walker kids dropped their baggage overboard, threw themselves overboard, smashed windows by carelessly throwing stones, and several times dropped treasured possessions, made you feel their parents were extremely unwise to let them out of their sight ever.
I don't think the scriptwriter meant them all to be incompetent fools; she just couldn't think, or couldn't be bothered to think, of any other way to make things go wrong for them.