After some legal issues some years ago, I no longer choose to carry a knife or three.
Now I look at non-apparent weapons, such as fans, cane, keychains, and recently I've discovered these really cool book place holder, which is built exactly like a sap-leather with a double-teardrop shape and a lead weight in the end.You lay it on an open book to keep it from closing when you're reading. It'll drop someone real good.
I also have these nifty flat, brass Chinese bookmarks, which without sharpening will still make a good slashing tool.
Someone once showed me how to sharpen the edge of the clasp of a wristwatch band, which when opened, makes a nice emergency cutting tool.
I had a ballistic pen...but I tend to lose things...
Reading Shibumi, by Trevanian was a real inspiration!