A break action shotgun, either single shot or double barrel, have certain advantages. They are highly reliable, durable, and their large barrels enjoy high recognition as potent weapons. The break action also allows the use of sub-caliber barrel liners which allow you to use smaller calibers of ammunition and to shoot it with more than adequate accuracy.

http://www.mcace.com/shotguninserts.htm

A 12 gauge break action shotgun with liners in, for example, .22LR and 7.62x39 (AK) would give you a weapon capable of taking on a very wide variety of jobs well.

Shotguns, with their ability to handle a wide variety of shells is, in itself, a jack-of-all-trades. Its weaknesses are that the range is limited to less than 100m with regular shells and to 200m with sabot slugs and rifling. Also the shells are both expensive and bulky. There are also issues with recoil and blast. A 12 gauge with a full power shell can be difficult for an untrained person with small frames to handle and even experienced people can have issues if the weapon is fired in constrained or confined spaces. Shooting a powerful shotgun shell while standing beside a concrete wall can be relatively painful, jarring and distracting if your not accustomed to the blast.

Most of these issues are mitigated to some extent by using sub-caliber barrel liners. A .22LR liner gives you the option to shoot the most common, least expensive, lightest ammunition available. The 7.62x39 barrel liner, or other roughly 30 caliber center fire rounds, gives you the ability to shoot at longer ranges, out to 400m, and gives you a round for deer-sized animals that is smaller, lighter and cheaper than most 12 gauge rounds and one that is less punishing in recoil and blast.

I personally favor the double barrel in 12 gauge. It gives you a shot and a follow-up. Should the firing mechanism fail for one barrel, an unlikely event given the simplicity and robust nature of the mechanism, you can shoot the other barrel.

Another option, a bit less expensive and more compact, but usually with less velocity and accurate, would be to use chamber adapters:

http://store.dinaarms.com/12_GA_Adapters_s/1.htm

Less capable perhaps than the longer barrel liners they nonetheless offer the ability to effectively fire a wide variety of shells with slightly lesser effect. This might allow you to more omnivorously graze the available ammunition supply and take advantage of less expensive, common or found ammunition.