This is the first of probably a very, very long list of "learn from my mistakes" posts to come.
Today, I went on a day trip with a friend to Saarbrücken, Germany. On the bus, we started chatting about carrying around our U.S. passports, and I was genuinely surprised when she told me she carried hers with her at all times. I don't, because I always worry about losing it; I also assumed that with open border agreements in Europe that I'd never need it for a quick day trip close to home. Plus, I've traveled in and out of the Luxembourg border countries several times and have never been stopped before.
Well, wouldn't you know it, just about ten minutes later, our bus was stopped by a police blockade.
The blockade was actually customs officers, doing a random sweep of vehicles entering Germany through that particular route. They boarded the bus to check things out and asked for everyone's identification, which of course, I didn't have (foreign drivers licenses doesn't count). I presented my drivers license and a card that contained my passport number, which they took to investigate, along with my friend's passport.
I was politely lectured that the Schengen Agreement (aforementioned open border agreement) only applied to Europeans, which I was not. They told me that if I were British, I would also need to have my passport since the U.K. is not part of the Schengen Agreement. And then they informed me that it was a good thing that I was an American, because if I were Russian and traveling without a passport, we would have real problems. (I did not ask them to elaborate.)
Fortunately, the fact that I did not have baggage, that I had a return trip bus ticket to Luxembourg, and that I was not carrying several thousand Euros across the border (I wish!!) probably all worked in my favor and the customs patrol determined that I was not a threat and let me enter Germany. Even more fortunately, the customs officers were all very friendly, polite and understanding in realizing that I'm just a stupid foreigner trying to figure things out!
So, lesson learned: carry your passport with you at all times. Even though you won't need it 99.9% of the time you are out and about, it's better to be safe than sorry on that .01% chance you are stopped and asked for proper identification!