Civilian Self-Defense Code of Conduct: To keep my equipment in good condition.
It is amazing how far and how reliable the shooting tools have become. Guns can take an amazing amount of abuse, left without cleaning after thousands of rounds and still perform reliably. About a year I was at a range with a couple of fellow shooters and one of them, a fanatical IDPA shooter, was using a Glock that sounded like somebody was applying a grinder to a piece of rebar. The movement of the slide was less than gracious too so I suspected that such gun was lacking a tad of lubrication. I asked the shooter when was the last time he cleaned his gun and he could not give me an answer other than in the last three months. The weapon as disassembled and to say that it was dry as a bone and dirty as my thoughts would be generous. After a quick cleaning and lubrication (I keep an Otis kit in my range bag that rarely sees action) the gun once again sounded and behaved like it was supposed to. The shooter confirmed that the gun was performing better, but had never thought about it because you know, Glocks are so reliable. And indeed, Glocks, XDs, M&Ps, FN-Ps and the whole gamut of guns that have come out in the last 30 years are perhaps one of the most relaible we will ever see, but that does not mean they are perfect or maintenance free. They are man-made machines that will fail eventually and even more so if the proper care is not exercised. So keep your gun clean and lubricated.
Also, your ancillary equipment must be in good condition. Holster, mag pouches, belts, speed loaders, etc need to be in working order and you must make sure they are. Never assume that because they do not have the same complexity of parts as a gun they will not fail. A simple turn of a screw (or lack of it) may mean the difference between a life-saving moment or an Oh Crap! situation. This also include your range bag and the items in it. Is your eye and ear protection in good working condition? If something is to malfunction, Do you have spares? Cleaning kits? Spare ammo? A first aid kit? Anything that will keep you practicing is necessary because it is practice what keeps you efficient as a shooter. I know this sounds like a shooter’s silly version of For Want of a Nail but it takes just something that stupid to turn a possible situation from just scary and survivable to a visit to the local morgue by your loved ones in order to identify your remains.