I hope OP doesn't actually live in a big city because he's probably screwed with what he has IMO.
My take on it, is you have a couple choices that each suck in their own way:
1. Drop everything and leave in advance or immediately when EVENT happens. You lose whatever sort of prep stuff you have by leaving quickly, but in many cases getting out immediately is the best way to avoid getting stuck, or the stuff that happens later.
2. Stay in place. Depending on EVENT, this could be short term or longer. Short-term probably would be the best time to just stick around in a city, where you could ride out EVENT without any sort of interaction with other people, given the proper preps - but, if you have no way of knowing how long EVENT will last, the city is not a great place to stay long-term. Where are you going to get water or food when you run out? Trade for it? Maybe, but you'll likely just get robbed or killed for what you have. Steal it from others? Again, great way to get robbed or killed. Stay too long, and you become a target of scavengers.
3. Wait for the exodus from EVENT to die down, and then try to escape the city. This is a great time for you to, again, get robbed or killed, and now you also have the added element of being a target of whatever law enforcement or government presence is there to maintain order. As was learned in Katrina and Boston, the government doesn't really like the idea of you defending yourself, even in situations where it's obviously the only answer. Going out on foot with a ginormous backpack and a rifle in the city is a great way to draw attention from all the wrong people. You may have a big nasty-looking rifle, but it only takes one guy to knock you off with a lowly .22 pistol from a smashed-in dark storefront window to bring you down and take all of your stuff.
People who got out of Katrina generally were able to do so because NOLA is a car-friendly place, and people could escape in cars or boats, but even then your vehicle becomes a huge target. There are numerous stories of people getting to their cars, and still having to defend their cars from roaming gangs. Some cities are more receptive to this than others. Places like New York, Chicago? Forget about it.
http://lonestar-mvpa.org/events/2005/05_Katrina.htmReally, the best course of action for you is to NOW begin adjusting your employment and lifestyle situation to remove yourself from urban living. A city is the absolute worst place to be during any sort of serious cataclysmic event. Cities are where people who have no survival skills, social skills, or morals tend to congregate.