Being a smart-arse
The issue with much of the advice given here is that ultimately, if the security people do believe that you are hiding something because you have tried to be clever, you are in a much worse position. Whilst I do not necessarily agree that one should hand over passwords or unlock a device when requested, sometimes acquiescing to the request is a bloody sight simpler and safer than not.
If you have a work laptop full of confidential material, then the likelihood is that they are not interested anyway. If you are working for EDF at Hinckley Point and travelling to Iran then you probably should be of interest, likewise on return.
It is all about the risk profile, put more markers up and the interest mount exponentially.
Get your down votes ready but this is the reality. Bluster on a forum can look good but when you are there, being asked questions by security people, unless you have something to hide, co-operation can go a long way.