.308 and 22lr
Best of both worlds, cheap and general purpose, get a Waffen Werks AK74 for about $600, a few commie magazines to go with it, and you can stockpile 5.45x39 surplus ammo in sealed tin for about 17 cents a round. Unless you expect to target practice a lot after things get ugly, one tin should last a very long time. (1080 rounds)
The round is cheap and effective, accurate to 200 yards and the AK is rugged and reliable in design and requiring little maintenance.