Jeez I'm going to sound like some nut-case survivalist, but I've been through a serious flood that completely screwed things up for the better part of three weeks. Our farm (where I grew up) wasn't hit that hard (except for the loss of power/services for the whole time) but when people who had lost everything showed up it got...interesting.
Basic "shelter in place" priorities are as follows.
Shelter - You need a viable place to stay, one that won't increase your risk.
Sanitation - You are going to need a way/place to urinate/defocate (usually at least twice a day). If the power is out (and water, etc) you won't have a flush toilet for long. A large bucket lined with heavy lawn/garden type trashbags that can be removed and disposed of as filled is often a good basic measure). You will need someplace to dispose of the bags as they fill. A lid and Baby powder to sprinkle in to help with odor is also a good idea. A lot of other personal cleansing can be somewhat relaxed but HANDWASHING is critical to avoiding illness during these sorts of emergencies. If water will be tight, have some baby wipes and/or waterless sanitizer available.
Water - You generally can't stay functional for more than three days without water. Rule of thumb is 1 gallon of drinking water per person, per day. (washing and cooking water is not included in this).
Food - Start with your perishables first (cook up what's in the fridge first) and then move on to your canned and dry goods. You should have a weeks worth of regular meals on hand. Rationed out, most Americans could stretch that one week of food out to two weeks easily. Consult backpacking sites for all manner of recepies and the equipment to cook them with. Proper ventilation is ESSENTIAL for using backpacking stoves, if you have a balcony or some outdoors place to cook then do it there or you could quickly wind up sick or DEAD!
First Aid - If you are sheltering in place in your own home then you probably have everything already.
Lights - Have an assortment of lights, and extra batteries for all. If you have candles and lanterns use them, but use them very carefully. A lot of people have burned themselves out while "sheltering in place".
Power - If you have a generator try to be stealthy with it. Run it as little as possible, during the day if possible, guard it while it is running, and lock it away securely when it isn't being used.
Be Prepared to eventually offer support/shelter/food/water and so forth to a few other, less prepared, people (who might even be your neighbors or friends), or be prepared to defend you and yours against them if things drag out because starving people won't care about your friendship or your family, just food.
ABOVE ALL - Be subtle about your preparations and stealthy when enacting them. If you have food/water, etc. and your neighbors don't, someone is bound to try and take it away from you (especially if they haven't eaten in 1-2 days and are getting hungry). Keep your lighting and so forth to an absolute minimum as a well lit place is a neon sign saying "we have supplies" and will attract all types.
A note about weapons - If you are afraid to use a deadly weapon then don't have one 'cause some more desperate person will take yours, kill you with it, and take all your stuff! If you are reluctant to use deadly force you had better find an alternative.
