The 30-06 military ammunition is still around, but even fresh ammunition is 15 years old. Commercial ammunition is available in all of these configurations. The recommended minimum amount of ammunition for any semi-auto rifle except the .22, is 500 rounds. You should stock at least 2,000 rounds for a .22. Shotguns of any kind should be ruled out, since ammunition weight and size preclude a reasonable storage amount and effective range is limited.
Many people think that storing various calibers of guns is best.
Think of the logistical mess of transporting three calibers, and their ammunition, in an emergency. The bottom line is to get a couple of the same identical firearms, pack a few hundred rounds for each, with plenty of magazines.