Here to the left is the green "North Face" backpack I bought for my trip to Japan a couple years ago. It's perfect for a week long trip the way I travel, which is very lightly. My sister recently gave me crap about it saying, "Sure you only carry one little bag, but you're wearing the same thing in every picture". Perhaps, true enough. I'm all about comfort and layers, so be it. At least I can carry my luggage around with me which gives me a certain sense of freedom when I'm abroad. If you're the kind of person that has 2 big suitcases with them when they travel, you should try my way next time. I've found it pretty great. Well this little green bag has proved to be a pretty great photo bag as well. I've got a couple expensive Crumpler bags (I really like my Crumpler bags, they're not cheap but they hold up and look cool) which I use much of the time (one backpack like this one and a shoulder type like this one), but sometimes I need to carry a bit more than just my camera and a lenses or two with me. The setup that can fit in this bag is what I used for most of the Drabbles shoots, which gives you some idea of it's versatility.
So what is it that I can fit in here? Well you might be surprised. Here's what I've got.
Canon 5D Mark II body Canon 28mm f/1.8 lens Canon 35mm f/1.4L lens Canon 580 EX II Speedlight Canon 550 EX Speedlight Canon Speedlight Transmitter Manfroto Nano Light Stand Speedlight umbrella bracket 36" Photek Softlighter 5 in 1 Reflector/Diffuser
As you can see, a pretty potent little system. 21MP camera with a couple lenses. As well as 2 lights with a wireless transmitter with a stand and umbrella. Plus if you've got an assistant you can have them hold the other light and shoot it through the diffuser as a second soft source. This is great stuff and these speedlights are surprisingly powerful, especially indoors. Sure I've got a Profoto AcuteB which might give nicer light. And I've got a crazy powerful White Lighting x3200 which can give a ton of light. But sometimes what you can carry with you is more important.
In conclusion, there is very very little that I can't do with this set of gear, AND I can carry it around all day while still keeping my hands free to pick-pocket people on the subway.