How to legally cross a US (or other) border without surrendering your data and passwords

Really quite simple:

‘…[I]n the current authoritarian climate, the [only] way to keep a government from using a border-crossing as a basis for acquiring your sensitive data without a warrant is to make sure that you do not possess, and cannot access, your data at a border…’

Source: Cory Doctorow, Boing Boing