First and foremost, it's important to not panic. Fear can take over and caue you to do things that, in retrospect, are dysfunctional.
Keep in mind that these preparations are intended to cover an assortment of disasters, in addition to possible end of society as we know it. Try to figure out the possible scenarios, so you can plan accordingly. (For instance, personal information on flash drive is portable, but if the electricity is out for significant time, unreadable. For certain situations, hard copy will be better-have both options.)
There are already a lot of great suggestions in the other answers. To these I'd add battery operated radio, glow sticks, well packed first aid kit (including ace bandages and antbiotics, if possible), spare cell phones, spare glasses, protective gear, such as heavy work gloves and solid shoes(for moving through wreckage) and filter mask (to filter out smoke, dust,smog, etc)
Maps and a compass may be needed.
I'd also seriously reccomend developing several rendevouz plans for meeting up w/ family and friends, to deal with different situations.
Please note that most of these items can be picked up inexpensively; and that the most important of these preparations are the ones that happen in your head...