Spare Parts Kits For Common Survivalist Firearms....
Some authorities advocate owning complete firearms in case of parts breakage. Not too bright when you can buy the parts most likely to break or fail for a pittance compared to a new or used firearm. Brownells.com and MidwayUSA.com are great resources for parts. In the 90s, I bought parts direct from S&W... Gunbroker.com and Ebay are also sources to review. Numrich Arms at gunpartscorp.com is another source. You can pay some hefty prices for obsolete firearms that weren't sold in large numbers.
Colt 1911 type pistols:
Magazine, extractor, sear, firing pin, disconnector, sear spring, ejector, barrel link pin. grip screw(s), firing pin spring, recoil spring. Nice to have a spare hammer, bushing, maybe a complete pin and spring kit. Wolf's spring kit is very nice value for the money. Maybe you look at replacing your magazine followers with arredondo or pachmayr followers, and put a recoil buffer in your slide system. Give some consideration to a Ciener .22LR conversion unit as they are affordable and make a great training aid and extend usefulness greatly.
AR-10 & AR-15 rifles:
Firing Pin, bolt takedown pin, spare assembled bolt or entire bolt carrier assy unit, carrier key screws; extractor, o-ring, spring and pin; ejector, spring & pin; gas tube & pin, gas ring set or McFarland ring for AR-10, Pin plunger and spring set for lower receiver, spare recoil spring, buffer and tube w/stock extension if use A2 or other full length stock. Spare gas block or A2 front sight assy (w/sight parts) also a good idea for long functioning potential. Roll pin can cup pin punches are worth investing in for dissembling gas assy parts.
M1a semi-auto rifle:
Firing pin; extractor, spring & plunger; ejector & spring, recoil spring, gas piston; gas valve spring, spindle & pin. Spare magazines.
Firing pin; extractor, spring & plunger; ejector & spring, recoil spring, hammer spring, magazine latch spring, trigger guard, gas piston. Spare magazines.
Ruger Mk II pistols:
Firing pin, extractor, recoil spring assembly. Nice to improve on factory parts with Volquartson or other aftermarket makers like Clark etc. Good to have spare springs and pins. Good to have a diagram for disassembly etc if you don't have your Ruger manual.
Ruger 10/22 semi-auto rifle:
Firing pin, FP return spring; extractor w/plunger & spring, magazine.
This rifle is capable of being tuned to extraordinary accuracy. Volquartson and others make a wide variety of accessory parts. Nice to have the extended bolt lock and magazine release levers. A picatinny rail gives interchangability to your scope system with other rifles. An aftermarket barrel and stock kit add much to potential accuracy. Very handy with short, heavy barrel and plastic or laminated stock.
Smith & Wesson revolvers:
Hammer nose & rivet, hammer spring, cylinder stop & spring, grip screw, sideplate screw spares, hand & sping. Wolf and other tune-up kits from Cylinder & Slide are very nice and easy to install. Kuhnhausen's manual is especially worthwhile for these handguns because so much of their interanals are/were hand fitted for functioning and there are many tricks to tune and assemble them correctly. S&W at one time sold parts direct.
Marlin 39 lever action .22 rifles:
Firing pin, extractor, ejector & spring, magazine tube complete.
Remington 870 pump shotgun:
Firing pin & return spring; extractor w/plunger & spring, R&L shell stop.
Greatly accessorized, these shotguns have pin sets, spring sets and tuned parts available readily. Ejector assembly and other parts reportedly have very rare incidents of breakage yet maybe you want a spare and the rivets needed to install it?
Winchester 94 lever action rifle:
Firing pin, hammer spring, sear spring, extractor.
Marlin 336 etc:
Firing pin, FP striker & spring; ejector & spring, extractor.
Remington 700 and other bolt rifles:
Firing pin and spring assembly with barrel shroud (for ease of installation), spare set of action screws, magazine spring, extractor with rivet (or extractor w/spring & pin if mauser type bolt). Spare screws for scope base mounts, spare sling swivel studs and qd swivels.
As far as gunsmithing tools, I've bought from Brownells over the years. Their Gunsmith Kinks book series is a good resource, as are the Gun Digest books of Firearms Dissembly, the NRA Gunsmithing series and the Jerry Kuhnhausen shop manual series. The Kuhnhausen books are the finest resource you can own if he wrote one for your firearms...
To install or replace parts, you'll need a lightweight gunsmith's hammer with brass face and nylon or plastic face. If working on S&W revolvers you will need cup punches of correct sizes. Brownells sells complete kits and in these kits you will find the individual parts identified by size. Buy what you need. Lots of intricate fitted parts in an S&W, get the Kuhnhausen manual for sure.
A complete set of drift punches from 1/16 to 5/16 will be handy for many weapons, especially AR type guns. Also want Roll-Pin punches, in several sizes. A variety of files, stones, and abrassives will enable custom fitting of some parts which will be necessary. Hard to beat a Dremel Tool with cut-off wheels and sanding disc setup plus polishing craytex tips and various sized grinding tips. A bench vise of about 6" jaw opening and a small Pony Vise or Pana-Vise will enable work holding of all sizes of parts or assemblies.
To do barrel work, you'll likely need a barrel vise and action wrench. Takes a lot of effort to remove a barrel from the typical bolt-rifle. The Brownells Action Wrench with interchangeable action heads will take a lot of pounding. Sako barrels and some Remington 700s I've removed seemed to have been torqued by King Kong... Removing AR-15/10 barrels from upper receivers is much simpler. A Strap-Wrench or AR Armorer's Wrench is the tool for barrel removal.
Probably the most useful gunsmithing tool you can buy is a Boresighting Collimator. I have a Bushnell #74-3333. This tool will orient your scope to bore precisely, enable first shots to be close to bullseye, and diagnose scope or scope mount problems. A great tool to own for many reasons.
Buy your spare parts kits, not a spare gun; unless you want a spare. If you get the spare, buy 2x the replacement parts. Ejectors, extractors, firing pins and springs do break or wear-out. Own the spares and know how to install them.