I noted earlier that the individual survivalist or group member would probably end up getting at least one supplementary gun. The type of supplementary guns one may need will vary according to needs, circumstances, and opportunities. The first supplementary guns should be ones that fill in gaps in your capabilities. For example, if you chose a short barreled carbine as your rifle in the core group, it would be wise to choose some kind of larger caliber rifle (longer range) as the first supplemental gun. If you chose a large automatic as your handgun, plan to add a smaller handgun as a backup if you plan to be in any potentially hazardous social situations where it may be inappropriate to carry a big piece of steel. If your survival shotgun is just a combat shotgun, add a long-barreled hunting shotgun, or vice versa. Additional training guns are also a good idea. These can include more .22s and airguns that can double as small game guns or loaners for last ditch defense.

In some cases, the supplementary weapons may not be firearms at all.  These alternative weapons can offer certain capabilities to the survivor.   The idea is to determine what exactly it can do for you and why.  If only that weapon can accomplish it, then it may be worth getting.  

Given that you may already have a good mid power assault rifle, you may feel that a higher powered supplementary rifle is unlikely to ever be your main rifle and want one lower cost gun to cover the rest of the bases.    That is where switch barrel and takedown survival rifles might play the role you are looking for.   Given if firepower is not an issue, you are probably not giving up anything to go single shot and the weight and complexity savings over additional semi-autos might be a good thing.  

The systems approach: Some survivors may want to supplement their basic set with a system of interchangeable guns or parts. An example would be to have a set of AK pattern rifles that serve interchangeably as the survivor’s main rifle depending on conditions:

A folding stock model for carry in a vehicle with cramped quarters where the user has little storage space but needs to have a rifle available.

An RPK style model with the long barrel, drum, and bipod for retreat defense.

An accurized "sporter" model with a milled receiver, trigger job, and a telescopic sight for hunting and sniping.

Low cost "standard" models as loaners.

Note that all of the guns can take the same spare parts and ammunition. They all take the same spare magazines, and the survivor only needs to learn one basic system for handling maintenance and repair. The survivor has a gun that is best suited for each situation while simplifying the training and familiarization needed for the hunting rifle, the car gun, and the bunker gun. The survivor prioritizes which ones are more important and gets them first, then the others as purchase opportunities arise. With some imagination, and money, the same approach can be done with the FN FAL, the M14, the Mini-14, the H&K series, and other rifles.

The system approach can also work with major components. AR-15 pattern rifles can use interchangeable upper halves and lower receiver assemblies that allow the owner to have a wide variety gun configurations by changing stocks, barrel length, receiver type, and even caliber. An AR-15 System owner can even get several rifles in different configurations just to simplify training and spare parts inventories.  A big advantage of the AR-15 system approach is that most people who have been in the military already know how to use one.  If you serve in the National Guard or reserves, you can limit wear and tear on your guns while training with very similar government issue rifles.

Shotguns can also lend themselves to the systems approach, since stocks and barrel lengths can be swapped around to produce different guns without altering the basic design. In any event, shotguns of the same make, caliber and model, but of different configurations, still offer simplified training, ammo and spare parts requirements. It also allows for the cannibalization of parts from gun to gun in an emergency.

There are some guns that fall into the supplementary category because of their special (limited) capabilities. These will be covered below.

Assault pistols  Backup guns  Hunting Rifles  Compact Shotguns  Machine guns  Submachine guns  Paintball guns  Sniper Rifles  Silenced guns  Black powder guns  Arrow weapons Grenades Grenade launchers Non-lethal Weapons Dart guns Air guns