In the absence of a safe I lock all our documents in a suitcase…,..yes, I know, the case could be stolen!
It is a risk we take with valuables though. Whenever there’s a safe, and normally they are the key code variety, I do use it. Obviously there’s a master code otherwise the hotel manager/cruise purser wouldn’t be able to open a safe that a customer had left in the lock position. Therefore, we simply have to trust that no one would access and copy documents or steal valuables. I guess that sealing them in a package might deter this as it would be obvious that it had been tampered with.