There's a lot to be said for going with all your gear to wherever the local college kids buy their backpacks and seeing which one most comfortably holds all your stuff. Get some Domke wraps to keep things from getting scratched, maybe get or make some individually-padded cases if you're the paranoid type (though the Domke wraps really are all you need), and call it a day.
Nothing screams, "Rob me! I'm carrying lots of expensive stuff that's easy to fence!" like an expensive camera case -- especially if it looks like it's loaded with heavy gear. But an el-cheapo backpack? Just a bunch of textbooks and maybe a baloney sandwich, and last year's entry-level laptop if you're lucky.
Bonus points if you toss the (empty!) backpack in a mud puddle, drive over it, leave it in the sun a day or two to dry out, and then toss it in the washing machine with a bit too much bleach.