[lb1lf]

Just put the phone in flight mode.

Wireless interfaces are deactivated, and any attempt at accessing online material is greeted with a message stating that you're offline.

[fuzzybeard]

Some apps won't let you access any of your content without authenticating with their servers. So even if it's local content, not having an internet connection would deny access. I can envision CBP saying they need to crack your phone to get to the local stuff.

[eridius]

What apps do that, besides games?

[riffic]

local data can still be viewable if the device is imaged and the content is unencrypted.

[pavel_lishin]

And watch the border patrol agent to make sure he doesn't turn it back off?

[riffic]

Require all searches to be performed in a faraday cage?

A better solution would be to disallow all searches of electronic devices since this seems unnecessarily intrusive.

[askvictor]

There is also the issue of cached data.

[compiler-guy]

Cached data is "physically on the phone", and so searchable within the scope of this policy.