I'll probably get branded as one a nut now, but, I'd do exactly what I already plan to do. Unlike I guess the majority of people, I have a disaster plan. I carry a pistol 24/7, even at work or at home, and in the back of my truck are 40 gallons of gas, a bag containing everything I need for 7 days as far as food, clothing and shelter go as well as a water purification kit. With the bag is are two sets of US military issued body armor, and a few changes of BDUs (everything is multicam, seemed the most appropriate.), a .308 hunting rifle and an AR-15 and a compliment of ammunition for both rifles and my pistols (pistols are all the same caliber, only 3 types of rounds between all my guns).
I've got 8 months worth of food and supplies to support 6 people stored securely (buried) at 3 seperate locations. One is near a house (I don't own, but feel I could appropriate and protect), a second is in what I consider a fallback location from the first, and the third is what I consider to be quite remote, all three have access to water, and reasonably close access to food. I rotate the food every 4 years and check the conditions of the supplies to replace as necessary.
In the event of a disaster, regardless of it's nature, if I feel that it has put me in a position to abandon my life as I know it, the first order of business is a hastry retreat to the first location, the only detour involved being to retrieve my dog (which I admit could be a hinderance to my survival but, I wouldn't feel right leaving her to die), afterwhich it's straight to the first location. I keep 4 maps with seperate routes in my trucks center console, each with multiple routes from different cities I've lived in or work in/visit regularly, generally seperate by direction of approach depending on where I am when things go south.
I've made provisions to allow 6 people to live for 24 months, however only one other person knows of my planning, and even they don't know where it is, I've agreed on a rally point with them, and promised them I'd check it every 7 days, afterwhich they'd be on there own. I have no intentions to retrieve family or friends, and assume the other slots would be filled with people I feel could benefit myself and whatever group we formed. I'm not a typically loving or empathetic person, I'd be looking for people that have no qualms about doing whatever it takes to carry on, stone cold without being sadistic. I have no reservations about taking from others to guarentee my own survival, even if doing so requires killing them or making their own survival impossible otherwise. If I were to take on a group, I'd protect them with the same fervor as I'd protect myself, and for that reason I'd keep that group small and functional.
If it were a civilization ending event as you described, my next step would be to find a self sufficient group, and implant myself and/or my own group as the law, by force if necessary. I'd offer protection from anything that comes, and guarentee safety in return for sustaining myself and/or my people, and I'd uphold that agreement with swift consequences to anyone who threatened it, insiders or otherwise. That'd be my position.
I don't care for growing food, I don't care for saving those who didn't plan ahead and can't help now. I wouldn't go to the lack of morals you see in most post-apolocalyptic stories, I don't believe in rape or torture and wouldn't stand for it. I wouldn't kill someone who left me with a choice not to, but not giving up food or supplies I need, or the threat of exposing myself to worse things (a party of even less poral people, for example), or taking part in things that destroy the group I'm with (stealing from within the group, killing another group member, rape, treason - whatever), I wouldn't hesitate to kill for.
Anyway, that's about what I'd do. I'll survive it if something happens, will you?