Hypothetically, if you had to pick just one caliber for everything what would it be? Lets say sub 500 yards and elk/moose/caribou/muleys/whitetails and speed goats. No reloading so factory ammo availability is a must. AND GO!!!!
caliber & cartridge would be a toss up between several. In fact there is probably several calibers that would be fine for any of the above. I'd probably say 7mm-08 or .308. My all around "if you could only have one" is a 12ga shotgun. Small game, waterfowl, big game...12ga can do it all.