The question is in the title of the thread. I find the limit of four to be a much more useful and interesting exercise for me personally. If the limit here were two things, then it would be a knife and a flashlight, and frankly I wouldn't feel too unequipped. These two items prove their weight in gold at least once a week. We already have plenty of threads about everyday carry where people list off everything without limits. Those threads are not that useful for me in my urban environment because I prefer to travel lightly, or rather ultra-lightly whenever possible.
I work from a home office and occasionally go into downtown for meetings in large buildings. I wear business attire. I have to make a decision on every single piece of gear. I often take the train (BART) into downtown, and I'm walking here and there, changing trains, etc.
I can't carry every "just in case" item, and I don't have room for too many backups. For example, I only have room for one set of keys and maybe one spare key for my car. I used to carry a spare plastic car key, but it broke inside my car door when I needed it most. (I won't be getting one of those again.) I don't have room for a lighter, or it's more like I don't feel I need a lighter. I have room for a knife or a multi-tool, but not both. I do carry a single AA flashlight and a fauxton light. I "use" the fauxton and keep the flashlight fresh. I carry a whistle, but have never used it in an urban environment, even though I've had opportunities. I understand the need for a bandana, but I no longer carry one. I'm talking ultra-light and compact here, and decisions have to be made. Anyway, if I really need a bandana, I can make something with the help of my knife.
Of course, my limits are self-imposed, but I'm of the mindset that being light, maneuverable, and inconspicuous is also quite valuable for survival in an urban environment. Traveling light also has an added perk of NOT being the biggest target of beggars. I am confident in my ability to improvise something out of nothing. I've done it several times in the past, and I'll do it again if the need arises. I can't even get close to carrying everything I'd like to have anyway.
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If you're reading this, it's too late.