One thing I always take is a 9 inch long monkey wrench. We were in Stuttgart a couple of years ago, and my friend's threaded headset for some peculiar reason locked up. All the shops were shut, and we had to catch our flight that day. The hotel we were in couldn;t find anything to help us. we were stranded. Luckily, we noticed a children's fair setting up, and one of the chaps had a monkey wrench that just fitted.
So now, my monkey wrench comes with us. It fits all the bolts on our vintage tourers, and it's big enough to use as a hammer, but not as heavy.