My 2.5 cents...
As far as light goes, lighting deters crime. A good Surefire is a must have, as for any type of defensive move, you have to be able to see what you are moving on.
Good pepper spray is an excellent alternative. The good stuff will stop a freight train, however, like a gun, it is only effective with positive contact.
If you want to carry a knife for self defense, carry a knife designed specifically for self defense as any real usage of self defense is going to put you in court, especially when using a larger blade and if you butcher your attacker in public domain. I recommend the Spyderco Civilian to everyone because without training, you can do a hell of a lot of damage. With training, you can do an unforeseen amount of damage. If you want to be faster to the draw, get it waved. None of those Benchmades are designed as a self defense weapon. The Benchmade Infidel is a defensive piece, as are a few fixed blades Benchmade makes including the 175 CBK push blade. The Cold Steel Grande Vaquero and a few other pocket pals are. The Spyderco Ronin, Yojimbo, Chinook, Gunting, Civilian, Endura Wave and Matriarch are. Additionally, if you are not carrying a crowned flashlight, you may want something to use as a close range, medium intensity impact weapon. I would personally place more emphasis on using the blade, as when you draw you best be willing to cut human flesh, and this is not something everyone is willing to do. I emphasize human flesh because in a real encounter, it would be just that, real.
There are things knives can and cannot do for defensive purposes. Just keep in mind:
1) A knife is effective for close range combat only, and indeed it may be the most effective close range weapon as knives when used properly in close range can be more effective than firearms as the mechanics of it as generally simpler and fewer things can go wrong. Karambit experts are probably the scariest users to see the damage they can do close range.
2) Drawing a knife from medium or long range can result in someone yielding a gun and shooting you (in other terms, you are provoking a situation). Subsequently, if you yield a knife in close range and know that an attacker has a gun, letting them simply run away to a safe shooting distance may not be a good option. If you pull a knife on them and cut them but still leave them in a mobile and functioning state, they are going to be more inclined to shoot you. On the other hand, one has to realize when your self defense becomes offense. Stabbing a guy 7 times in the back who is trying to retreat looks very bad in court. I present this situation because it is lose/lose situation and the line between continuing combat versus ending an engagement is a very light shade of gray.
3) If an attacker sees you have a knife but believes you will not use it, they will continue on the offensive side and it is not uncommon for them to try to take your weapon from you which is the absolute worst case scenario. I do not abide by the intimidation clause as if that fails, you need a backup. It is like flashing a gun without bullets; indeed it works some of the time, but when it fails, it can get you killed. If you are going to draw it, use it, and use it effectively.
4) It is a unique experience to cut human flesh as it is so personal. In many respects, the thought is repulsive and some people cannot bring themselves to slice open another human being. If that is the case, do not draw your knife in a self defense situation. I say that all so bluntly for a reason. You must be willing to literally carve someone apart and accept the fact that they could die in front of your eyes and whoever else you are with. When someone gets cut up, it is not a pretty sight at all. There will be both legal and moral consequences if you use a blade for self defense.
5) Encounters involving using knives as defensive pieces are quick unlike the media publicizes so I suppose fighting knives may not be a good term as you only really need to make one advancement for something to end. For example, a user knowing where the carotid artery is and being able to slice in that area is going to end an engagement very quickly.
Notice where the carotid arteries lie and how protecting them, the chest and belly is practically impossible when actively attacking. There is no exceptionally effective way of shielding this vulnerability, even with many modern armor advancements. A larger blade with a skilled user will quickly find an opening and that is the means to the end. If someone's carotid artery gets sliced open, they are going to die very quickly.
6) Non lethal usage with a blade is ideal, but this is far from the common case. Humans are fragile creatures and if you slice or stab into one, there is a chance they are going to die despite current medical technology. Using non lethal self defense, say cutting the leg or arm, is indeed ideal and you may have openings to do this...on the other hand, you may not or your adrenaline may compel you to go straight to lethal self defense.
