Bitcoin.
I know, everyone can make fun of me, but it is portable and can easily crowd borders.
Lots of American don't get it, used to carrying around King Dollar. Most of the rest of the world knows better. The smaller and weaker the country, the better Bitcoin looks versus the domestic currency. Ironically all the Bitcoin venture money is going into US companies, but that's mainly because Bitcoin itself can be trusted even certain US govies can't be.
I agree. Bitcoin is a way to prevent confiscation of your money by the greedy .gov. If you previously established a bitcoin wallet (like Electrum) whose seed is an ordered series of words (12-24 common words), you could cross the border stark naked, and retain control of your dough, assuming you have memorized the seed.