My go-to not-a-gun is a knife. My knife of choice for about two years now is this Fox Karambit. The knuckle ring makes it easy to pull from a pocket. The wave of the backside of the blade grabs the edge of a pocket, and it opens one handed as it is drawn. While the blade isn’t long, it is one hell of a self-defense tool.
In situations where something less threatening might be better, I like the Spyderco line. They are still easy to open with just one hand. This monster has a huge blade for a pocket knife. It locks securely, opens easily, and (as you can see from the state of its blade) is actually a useful tool for everyday carry. This one is a Resilience, and it has held up great through three years of abuse.
But if you’re flying, or visiting the courthouse for jury duty, you may not be able to carry a knife, either. For those moments, I recommend you have something else you can keep in a closed fist. This karambit bottle opener ( The Bottle-bite) from Max Venom is my favorite. The aluminum is strong enough to stand up to a punch, and it isn’t too obvious on a keychain.
Pens are useful, too. While I own several hardcore fighting pens, they are not subtle. And I’ve heard stories of them being taken because some (mostly TSA agents) felt they were threatening. I like the Zebra pens. They have stainless barrels, and rubber accents. They’re smaller than I’d like, but cheap, easily replaced, and they’re decent pens, too.
The last of these could get you in trouble. It could also save your ass, if you needed it. It is a fiberglass and epoxy resin. This one is made by TW Brands Gear. It is seriously sharp. The black on the blade is where it is rubbing on the kydex sheath. It fits tightly, is easy to hide, and isn’t going to set off a metal detector. It will, though, show on body-scans.
All of these have their strengths. The one weakness is that you have to be within contact distances to use any of them. But if you need an edge, you take one where you can get it.