The challenge with planning for SHTF, is knowing what kind of S to plan for.
Meteor/Comet impact, eruption of Yellowstone super volcano, economic collapse, civil war, ... All are possible, to varying degrees. But may require different types of preparations - depending on your location.
For example, I have land in Montana that could be a great place to sit out an economic collapse, but a terrible place in the event of a Yellowstone eruption. By the same token, my land in Florida would probably do well for Yellowstone, but is likely a bad spot for an economic collapse.
How can you even plan for a Meteor/Comet impact? So much depends on the size and impact zone. A relatively small impact in the Pacific or Asia, and I'd likely want to stay in Florida (since it's likely to trigger at least a mini Ice Age, and possibly a full Ice Age). Then again, an impact in the Atlantic could make staying in Florida suicidal. Plus, past a certain size Meteor/Comet impact, no preps are needed - as they'll likely be no survivors.
So, how should one plan?
Personally, I have two plans. One set of plans and preparations for sitting it out here, and another for relocating in a hurry (aka bugging out). Truthfully though, in any large scale and long lasting SHTF incident all either plan might do is slightly increase my chances of survival.
So, maybe the best course is to prepare for relatively a short term, localized SHTF. Storing extra food, water, money (preferably real money - gold and silver), and the means to protect them, might be the way to go. These things are always good to have on hand in any event.
The decision to make more elaborate preparations for a long term large SHTF (or TEOTWAWKI) situation is more difficult.
Whether to devote extensive resources to prepare for a situation that may not occur in your lifetime (and may not be survivable if it does), is a question with too many variables to yield one answer for every person. The answer for an urban dweller with little or no surplus income, would be very different from the answer for someone in a rural area with arable land and lots of disposable income. Most people probably fall somewhere between these extremes.
Personally, I'd recommend each person do what he can comfortably afford to do - and what makes sense for his individual circumstances.