If I were in an urban setting when TSHTF... well, I guess that I won't be taking my BOB with me. Tomahawk... well, I could probably carry something that makes self-defense both easy and all you need is to move your hand...
The Wrist Mounted Flamethrower*
Who here thinks this would scare away anyone who didn't have a gun? You'd need a safety measure to make sure you didn't accidentally set it off, though...
*I don't recommend this unless you're willing to risk a small burn...
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Besides that awesome flamethrower... I guess you could put George Bush stickers on a backpack and no one would ever even think about stealing it
Now I'll be serious... knife in your pocket, sheathes attract attention. Gun in your pocket, and please make it small, nothing big. Dirty (just has to look dirty, doesn't actually have to be dirty) clothes will probably make you less of a target, and if I were you I wouldn't carry a backpack. One of those small Sports Bags (those small synthetic ones with the draw strings) would be okay... just don't make it look like you've just come out of a nice, clean apartment.
And grow a beard and try and look like a homeless person. You might not be as much of a target... as homeless people, you know, can't usually afford much.