My $0.02

Following up on what CJK said ... you can buy soft armor ballistic pads online. I've got a couple that are about 12 inches square. They're not cheap, but they're also not as expensive as a full armored vest. Just get a couple of the pads and use them to line your backpack. It's unobtrusive. In the event of a hold-up in a disaster zone, you've got some minimal protection if the robber does shoot you with a handgun. Of course, you've got to be able to use your backpack as a shield - if you don't get it off in time - you're dead anyway. With the ballistic pads and the backpack material - it might work against most handgun bullets.

As several people have pointed out - this won't stop a rifle bullet. Use common sense ... which is always the best protection.

Pete2