Mossberg 590 with bayonet lug (and bayonet). Plus small .22 semiauto handgun, like S&W 422, and then something with a 4 in it, revolver or semi. Then any bolt action .22lr, and maybe some cheap bolt action centerfire, maybe in .223.
Stick to ammo that the military uses or is cheap and plentiful.
ping
But if I had the option of having five, I'd take: a 12-gauge shotgun (pump or semi-auto, whichever you prefer), a .22 handgun (a Ruger Mark II target pistol is inexpensive, accurate, and reliable), a 1911A1 (that .45ACP makes really big holes), a .22 rifle (any semi-auto would do fine), and an SKS (preferably a Russian-built).
If you shop around, all five of these firearms can be found for under $1500. Ammo for all of them is relatively inexpensive and can be found at just about any sporting goods store, gun shop, or department store (plus a number of gas stations in certain parts of the country).