Personally, I don’t take this particular approach. Most people will make themselves a 72 hour kit. I took a survival training class in college where they literally took you out to the wilderness and you could do what you had to do or starve. Not a bad experience. But if you are in a disaster, or even if you’re not, sometimes, it’s good to have a 72 hour kit around, which many learn about in health and safety training.
A 72 hour kit can be found in many forms. Some stores put them together for you. Other outdoors stores like Cabelas just sell the individual pieces, because there are so many possible combinations. The first major thing to get would be food and water. I’m not sure how much good this would do for you if you were trapped in a building, because chances are you left it in your basement or your car. But it’s one of those take it with you things. If you have it with you, this food and water could be essential to survival. Second, you need bedding and clothing. If your clothes get wet or something like that, it is better to have a dry set, and you should have things like a raincoat or poncho as well as emergency heat blankets and possibly even sheets.
It’s best to have a flashlight or light of some kind such as flares, candles, or a lighter. Your phone does not count unfortunately. And you should have some basic equipment such as a can opener, utensils, shovel, radio, pen and paper, axe, pocket knives(they have quite a few options), rope, and duct tape, because after all, duct tape fixes everything!
With this in mind, you can buy on your own and try to figure out which one works for you. But there are quite a few organizations, groups, and of course health and safety training programs that can give you tips and advice on how to put together an effective and necessary 72 hour kit. They can give you a good sized bag that is manageable while telling you the best things that you can get to maximize your space and yet still be able to have with yo9u quite regularly just in case you have the need for it.