Would you say more about your employer suing you if you cave under pressure and unlock the laptop? That sounds to me like your employer is asking a lot of you! Or, if you are bluffing to security about the suing, why are you putting your personal safety on the line to protect your employer?
It's a weighing of risks, really. I don't value neither airport security or my employer's secrets as highly as my own safety but will weigh in the risk as the situation develops.
If I am asked to accompany them to the dark room I'll just give up, unlock the laptop, hand it to them and then quietly inform my employer's legal team that a potential security breach has occurred (after I get safely to a hotel).
I really don't want to spend time in jail because of a nervous cop.
Yikes, I hope you are well paid! (Re: 1 and 3. 2 is table stakes in this day and age. In fact re: 2, would you be willing to share a scenario that calls for sneakernet by courier vs a network storage/transfer?)