My original dSLR kit was the K20D camera, DA10-17, DA18-250, FA50/1.4, AF360 flash, and Raynox DCR-250, all stuffed into my large teardrop Ameribag (doesn't look like a camera bag; is easily defensible; has inside pockets) and it did me well on a long journey across Mexico. I'd now update that kit: leave the AF360, replace the 10-17 with my Tammy 10-24, add my Vivitar 24/2 and Sakar 500/8 mirror. The 18-250 is my basic drive- and walk-about lens; the 10-24 is for small spaces; the fast lenses and small mirror, as needed. And a P&S, for when the dSLR is inappropriate.
I got the Ameribag after having my pocket picked in Guatemala. Luckily I only lost my wallet, not my P&S. Ask me about how it can foil pick-pockets and bag- and strap-slashers.
Some will argue that the 18-250 is too long for Euro-size cities and towns. I disagree. I've shot in small villages in Germany and Mexico with long lenses, and in cramped vertical Arizona mining towns; and I wished I'd had longer glass in villages in Italy and Guatemala. The long focal length lets me capture details that are otherwise inaccessible.
And my 500/8 mirror lets me grab otherwise-impossible people shots, and striking juxtapositions. I used it to good effect just a couple days ago in the crowded plaza here in Santa Fe NM, where I am this month. It would be even better in a hillier town. I originally got my Lil'Bigma 170-500 for people-shots in San Francisco, but that's not exactly a good travel lens.
So, my recommendation: The DA18-250. Something wide. Something fast. A Raynox. All stuffed into an Ameribag along with wallet, pills, collapsible kite, notepad, hat, a smashed-flat roll of toilet tissue, flashlight, calculator (the universal translator!), hand sanitizer, lens- and sensor-cleaning kits, extra batteries and SD cards and shoelaces, map, etc.