One very handy item in a Urban BOB (or any BOB) would be a compass. Getting lost in the concrete canyons is as easy as getting lost in real canyons. A compass can (at least) let you know if you are traveling in the right direction in unfamilier areas.
+1! A lot of people assume a compass is only to be used outdoors. But it's very easy to get lost in an unfamiliar city, especially abroad. My compass has made life a lot easier on many occasions even though some of my buddies thought I was a little crazy carrying one in the middle of a city. That is, until we ended up in some maze of poorly signposted streets.