A lot of my work is offsite, so I have most stuff packed up in boxes.
Two of these:
http://www.homedepot.com/p/RIDGID-22-in-Pro-Tool-Box-Black-222570/205440481
One holds my nail bags and a few misc items such as extra hammer, pry bars, etc.
The other holds all the misc stuff that you 'sometimes' need on a job (measuring tools, etc) along with electrical tools.
One of these:
http://www.homedepot.com/p/RIDGID-22-in-Pro-Gear-Cart-Black-222573/205441921
It holds most of my cordless stuff
Two of these:
http://www.homedepot.com/p/RIDGID-22-in-Pro-Organizer-Black-222571/205440492
One holds a cordless drill, cordless impact driver, bits, etc.
The other holds some hand tools -- wrenches, sockets, pliers, etc.
Also have 4 or 5 of these:
http://www.homedepot.com/p/RIDGID-22-in-Pro-Box-Black-226036/206291778
All my concrete/mason/brick tools in one, the others are for fasteners. One holds plastic jars of assorted screws, the other nails. Nails for pneumatic nailers are in the other 2.
One similar to this:
http://www.homedepot.com/p/Husky-35-in-Mobile-Job-Box-222167/205053257
Air hose, brad nailer, pneumatic stapler, 2 framing nailers.
Then I have a 24x24x48 job site box, with all the stuff that I usually only need on a big project, or rarely...I just set it on the trailer with the tractor forks when needed. Big drills, hammer drill, jigsaw, belt sander, etc. Most stuff in this box is in the whatever plastic box it came in, or a zippered soft case.
The nice thing about the rigid boxes (and there are other systems similar...dewalt has one, milwaukee, etc) is that they stack, and lock together. So you can stack them on the cart, and latch them, and then roll wherever you'd like to go. (It would be nice if the cart wheels were bigger, though, so you could go over rough terrain, or up steps easier.)
I've been using this system in it's current incarnation for a couple of years now, and it has worked well. But again, most of my carpentry work seems to be off-site, so I need an easy way to just either grab component boxes as needed (i.e. if I am just helping somebody else frame something, I can just grab the box with my bags and maybe a saw.), or to load out a lot of stuff in the truck or trailer.