For a SHTF situation, more things can go south than just food and firearms.  Fixing and patching structures, vehicles, and equipment will be important. 

Please note the difference between fixing and patching:  fixing is repairing or replacing something in a "done right" manner--what you would expect a professional you hired to do, while patching is a temporary or less desirable solution to a long term problem.  Putting new glass in a broken window is a fix, covering it with a board or plastic is a patch.  Retapping buggered threads in a scope mount is a fix, cross threading in a screw with some loctite is a patch.  Both are important, and it is worth understanding when a bad solution to a problem is better than no good solution to that problem; a dripping pipe is better than a gushing pipe, a loose gunstock is (probably) better than a missing gunstock.

Some material you may use is heavy, and stores well with minimal  care, such as nails, bailing wire, lumber, rope or cordage, tarps, tar paper and plastic sheeting.  Other supplies have definite shelf life, or more require controlled storage conditions, including tape, glues, solvents, hoses and belts.  Keep an eye or your supplies, buy some new stock now and then to cover shelf life issues.  The problems you may have to solve vary with area, equipment, and particular situation.  Look for supplies that can do more than one thing, are inexpensive, and store well. 

The tools available may also not be ideal, and it is worth having alternatives that will work when systems start going down.  A few years ago there was a SHTF show on TV that featured "survivors" trying to rig up electricity so they could use tools.  Bulletin:  people used tools before electrical tools existed.  Hammer, hand saw, pry bar, screwdriver, hand drill or bit & brace, bow saw, axe, star drill, sledge, cold chisel, wood chisel, file, rasp:  these things are your friends, store well, are not too expensive new, and can usually be found at yard sales or thrift stores. 

Common materials and some of their uses:

1x2 wood:  buy 1x2 in 8' lengths from lumber stores or home centers.  Available in strapped bundles for low price and easy storage.  useful as battens to hold sheeting in place.  Roll one edge of the sheeting around the first batten, then screw or nail it in place.  Add more battens to secure the sheeting and keep it from flapping too much.  Use for emergency storm windows, or roof repair.

Wood plugs:  buy premade tapered wood plugs from marine supply store, or make your own.  Turn them on a wood lathe, or just whittle them.  Pretty is not important, just the ability to bang one into a hole.  Best made from softer wood, and stored very dry.  Dry plugs will expand when they absorb liquid, improving seal.  Have a variety of sizes.  Possible uses include plugging broken pipes, or fuel tanks.

Solid wire:  baling wire, tie wire, stainless lock wire, bare copper, and fence wire can all be used for a variety of things.  Take a bunch of wraps and use as a subsitute hose clamp, wrap a broken gunstock or tool handle, use to secure a "plate and toggle" patch, take enough wraps and it can be used in lieu of a shackle or lifting sling.  Bare steel wire, such as tie wire can be used as a filler metal for welding. 

Solder:  soft metal alloy, can be used for some metal repairs, can also be stuffed into holes with buggered threads.

Nails:  One size does not fit all.  Most nails are sized in pennies (d), more being bigger.  16d and 8d common nails are a good start, with a few boxes of roofing nails (large head). 

Wood screws:  now ubiquitous drywall and deck screws are harder and more brittle than traditional screws, and can be pounded in like nails. 

What has worked well for you?  What issues do you face for your location?

  One thing for EVERYONE to have.  Now we have some better stuff, due to being a ranch/farm (such as an actual portable air compressor.etc.).

   Tire repair:
  Plugs, plug pusher (A t-handle, not a stupid screwdriver handle) and a rasp to rough the edges.
 Tire PATCHES, and irons to remove the tire from rim.
  Glue for the above patches and plugs.
   cigarette lighter plugin Air Compresser.

  Tires are a big thing not always a tire shop around.  We keep tire repair supplies on-hand due to all the fixes we do, extra tube, actually have one of those "bolt down" tire changers, air compressor,etc.   For as often as most would use it, the above would get you by for emergancies.

 As for our house:  we have a mediocre fireplace, but we're actually getting a wood STOVE put in as soon as it warms up.  We've got sheets and plywood to block off some parts of the house (in event of a pwower outage) to heat less area.

I have often thought about getting sheets of plywood and screws to secure the house if need be but have put it off...thanks for getting me thinking again...just a few sheets every payday would probably add up in a few months to a considerable stockpile...

 I always wanted a concrete blockhouse with steel shutters 

As a rule, people in this country don't use intelligent design in building houses. Initial looks are much, much more "important".

Best.  Ever.  Use.  Of.  The.  Term. "Intelligent Design." Ever.  You win the internets! 

How about also adding rope, string, and bungie cords?

Back during the 2004 hurricane season here in Florida, blue tarps were everywhere on rooftops.  Bungie cords are one way of securing the edge of a tarp, and they're helpful for other routine kinds of things too.  Home depot has big plastic jars of them for not much $.

I saw the ideal SHTFALL structure the other day:  a multistory concrete box with steel shutters on a hill in the middle of a clearing in the middle of nowhere.  I got all excited, then someone told me it was a rural fire training station.  I'm requisitioning it when the zombies come - that thing was DESIGNED AND BUILT with the sole purpose of withstanding disaster!