You can just pull the whole bucket with your gear and use the bag by itself. And these babies are made so well. Even though a soft case, I have landed (details ommitted here on vehicles numerous times. My photo gear has never suffered a scratch. I have fit a D700, 24-85 and ringlight in a bucket no problem.
I do not bike with gear very often.. but if I were to do it, I would either use my crumpler photo backpack, or pick up a bucket to use with my barney & rustle (messenger bag)
The messenger bag sits on my back far better than any of my MDH's do (crumpler million dollar homes), but If I wanted to use any of my MDH bags, a quick addition of a cross strap like the barney and rustle bag has (there are loops that would work to attach it) would make it more than usable.
I do not commute with my camera much, but have been on a couple of cycling trips
(~two weeks of riding each) and the camera (5D + 24-70/24-105) was on my back
each of those days. I've used the lowepro SlingShot 200AW, but I use the bag for
other things as well so it's a bit large for this purpose (the 100AW is smaller and maybe better.)
If you need other stuff in your bag as well, then the lowepro fastpak 200 that has
an upper compartment for more regular stuff.
These are 'traditional' backpacks though and you may want the crumpler slingshot bags for cooler looks
I am checking this bag and it looks like it can handle what I need to carry and even more. I wonder if the velocity 8 or 9 will be enough.
Just having some doubts on sizing.
The gear I want to carry around would be a 5d + 24-70 +70-200 2.8 on heavy carry days and a 5D + Tammy 24-135 on light ones. The 9 sounds good and the 8 fair for this amount of gear, maybe a bit tight for the heavy days
on vehicles numerous times. My photo gear has never suffered a scratch. I have fit a D700, 24-85 and ringlight in a bucket no problem.