I travel a lot with work around Europe and the US and always take my camera with me and this has taught me a few lessons.
1. Pack lite and make the most of the kit you take with you. Trust me walking around with all your glass is old really quickly.
2. Pack lite, unless you want to risk having a horrid trip because of lost equipment ALWAYS hand carry your camera...this poses the weight problem as most flights are now putting a 10kg limit on carry on (and some as low as 6kg!)
3. Cheat where possible. How many shots do you think you are really going to need 200mm for when walking in a city? I live in London and shot in the city at weekends and to be honest some of my most preferred shots have been at <100mm and so the 24-105 is a great choice for this...plus if I want one or two longer shots I have a 2x tele converter (no idea, but better then lugging a great 70-200 around!).
4. Be creative, get out of the comfort zone of having all the kit to cover everything and use creativity to overcome the short falls in traveling light.
Personally I now travel with just my 5d3, 50 1.4 and 24-105 and the 2x tele. I don't even bother with my flash as the 5d3 can make up with it in ISO. Sometimes I might add a fold up reflector and a cheap (See:lite) 70-300 5.6 for when I think I will REALLY need some reach, but it is a fraction of the weight of the 2.8 version.
I also take my mac air with me as carry on, this acts not only as a backup for the memory cards, on location/hotel room editing but I also use it as a charger for many devices (cell phones etc) thus saving the need to carry a lot of adapters. A second battery will generally see me last a two week holiday as I do not use live view much at all.
PS, if you want a quick and dirty of the tourist highlights in London, there are a number of walking "photo tours" run for photography training purposes which are worth investigating.