There's about a million answers to the bug-out bag question. I agree that a backpack is good if you're going to be hoofing it at some point.

A duffel bag or storage bin is good if it's just going to sit in your car or house. Or maybe augment your backpack BOB.

I like Maxpedition's offerings because they have a zillion pockets and compartments for organizing everything. The big thing with a backpack is to try to test it out in the store and see how it fits first, if possible. I've had a couple I had to return because of the way the pack felt when wearing it...