On my 2007 trip, which covered Scotland, Northern Ireland, Ireland, France, Belgium Netherlands, Germany, Austria, Switzerland, Spain and England in four months, I carried an XTi, 10-22, 17-85 IS and 70-300 IS and picked up a 50 1.4 in Paris for poorly lit museums. The 17-85 was my work horse doing about 85-90 percent of my shots. The 10-22 covered nine percent and the 70-300 barely edged out the 50mm for last place.
Earlier this year we returned for a month, mostly in Italy, and I used a 5DM2, 15mm fisheye, 16-35L, 24-105L IS, 70-200 f4 L IS and extenders. I did not carry everything all at once except in transit. Mostly I carried on a daily basis what I suspected I would find handy. Vatican and Coliseum were good fisheye locations, but I made certain to mix the lens use as much as possible. A photo vest with padded pockets was my daily bag.
I make good use of a monopod and have a lightweight Gitzo tripod that is very compact for those rare times when I really need one, like night shots.