I forgot to mention the 1.4 extender...
And the 50 1.8 stays home all the time, that was one of my first lenses I got, it is the best lest to learn with, with it not been a zoom lens it pushes you to play more with compassion, and with a 1.8 opening, it is great for low lighting, and great on DOF...
I do not have a problem taking it with me all day, one thing that helps a lot is to use a grip, it helps to have a better support on your hand, and it adds the second battery, I just love that lens, I try to use it all the time. I have been out, all day, with the 7D griped, 70-200 2.8, 580exII on a R strap all day at the zoo, or the city and I have done ok, do I feel it, sure, is it doable, for sure! Maybe been 6' and 250 lbs help...