Step 1: Stock up on snacks. We're not talking about just any snacks, we're talking about the essentials: Cheetos, Pop-Tarts, and 2-liter bottles of Coke. You know, for the long haul.
Phase 2: Stock up on more snacks (and possibly a few extra pairs of pants, just in case).
Survival Hacks for when the going gets tough: how to MacGyver a toaster into a makeshift solar panel, and other essential skills.
Remember: DOOMSDAY IS NOT JUST A SURVIVAL GUIDE, it's an ART FORM. You must be willing to think on your feet, and on your back, and maybe even on your head (just kidding, that would be weird).