As important as food, water, shelter, and security are, I’ve been discussing them largely in the absence of what is likely the very most important factor in apartment survival. That factor is the presence of the other people in your apartment complex. Depending on the circumstances, those other people may be a help, hindrance, or outright danger to you. The other people in your complex will determine the longer term viability of bugging in to an apartment.
First, let’s look at some broad classifications of people that you’re going to have at your apartment building. The first type will be those that believe everything will be better tomorrow morning. They will wait for the water and power to be restored, and are sure that the bus service will resume tomorrow so that they can go to the grocery store. They may also be extremely frightened and agitated, and could be dangerous if armed. I would expect this group to have the lowest overall survival rate.
The second type will be the G.O.O.D. type, whether they are preppers or not. As a crisis looms and deepens, they will pack up and head off to find safer, better situations somewhere else. They may or may not take all of their resources, and if you have exposed possessions, they may or may not take some of yours. What is more, they might not stay gone. It is entirely possible that a proportion of them will find nothing better out there and survive long enough to make it back ‘home.’
The third group are the ones that while perhaps not prepped, are proactive and coping as best they can. They will be among the first to start pilfering empty apartments for food, water and resources. They may be jerry-rigging solutions to things like heat and water purification, and they might even be a bit territorial, and perhaps somewhat aggressive in some circumstances. I would expect this group to do better than either of the others.
Finally, there are you and hopefully one or two more people like you. But there are no guarantees of that.
So for you, the first question is to find out who stayed and who left. When you know who is left, you can assess them as to whether they are threats or possible comrades. Remember, threats need not be limited to actions directly against you. It might well be that the neighbours are being a threat because they will not make proper sanitary arrangements, or making too much noise or light which may attract unwelcome attention.
It is imperative that you find like minded people in your building as soon as possible. Everything I’ve discussed can be done more easily by a small to medium sized group than can be done alone. This may require you to make the first overture, and will likely necessitate you taking a leadership role. Depending on the depth of the crisis, you may need to make decisions (or guide your group into making the decisions) for everything from defense and rationing to water and sanitation. This doesn’t give you license to become a feudal baron, but you will find that in a crisis, people will rally behind someone that is willing to step up to make those decisions, as long as the decisions are sound.
A small group working together will greatly increase your chances of survival, and group pressure will likely bring the ‘unwilling’ into line and into your group. The flip side is that a building full of uncooperative individuals makes it almost certain that all will fail. Despite everything you try, you may fail to weld the remaining people in your apartment into a cohesive group.
I see no easy answer to this, short of relocation. If you cannot get everyone in your building on side very quickly, the viability of staying at your apartment is severely diminished. Whether it is an empty building or storefront, an abandoned house, or a multiple unit such as a four-plex from which all have fled, you and whoever is like-minded need to go. You may even be able to find a building that is working together to join, but I believe strangers will have a difficult time getting in to a functioning group unless you possess goods or skills that are needed.
In the final analysis, the determining factor as to whether or not apartment survival is a viable option will come down to who is left in your apartment, and whether a community can be created from a collection of what were likely strangers before the crisis.
It is on this that all of your other efforts rest.