European PJist have used Billingham bags for decades & even if this wasn't so, they look expensive & I wouldn't suggest using one of those. I love working out of Domke bags, but as down & dirty as they can be they still look like camera bags. Once their loaded up every camera bag I've ever seen looks like a camera bag.
I suggest a backpack. The LowePro Stealth has a slim profile, but they aren't so easy to work out of & I'd rather carry a laptop in another bag due to the weight.
I've been considering the Lowe-Pro
Rover Plus as there is some abitity to work from the bag without putting it down, but you have to decide if it's big enough for your gear. These Lowe-Pros have a top & bottom compartment & you can put Domke dividers in the top for additional storage with quick access. I cut the logos of any gear possible & Lowe-Pro's come off easily.
If you don't mind putting the backpack down, Delsey's
Pro Digital 33 is roomy & waterproof. The Rover Plus is more stealth & would probably be more comfortable for hiking all day, but most any backpack is easier on your sholders than a camera bag.
Regards,
Bern Caughey