I can't stand wasting so much time trying to decide which lenses to bring, which is why I try to own as little gear as possible. Last summer I just kept my Think Tank Speed Freak bag loaded with my 5D2, the f/4L trio, a 270EX and a 50/1.8. That was pretty much all I owned for Canon at the time, it went with me everywhere, I never had to think about it, and it was all lightweight enough to just take without thinking. Awesome!
And now I've gone and ruined it all with a secondary body and an extra prime, with one more prime and probably another zoom too. 
Go to setup is the 24-105L on my 5D2. Rarely need wider than 24mm, and if I need longer than 105mm I just make sure I'm in 21MP mode and crop as needed for a tighter composition.