The Flag's a Plus

I've been rethinking my personal threat model due to wholesale scanning of electronic devices at the U.S. border. I think I've figured out a few things that I can use that might be useful for others. The problem is this: Currently, Customs and Border Patrol (CBP) is scanning devices, but they are not scanning data that's not on the device or not directly reachable with the device. This is due to their interpretation of Riley v. California -- a U.S. Supreme Court decision that said that law enforcement can't use credentials found on the phone to gather additional data without a warrant. If they're suspicious (or if you annoy them), they can seize your phone. So, I need to be sure that my phone is "disposable" and I won't lose any critical data. Wiping my phone might work, but there's some information that I'd like to install on my phone before I leave (phone numbers of people I'll be visiting, for example), and if searched, a wiped phon...