I have seen many deer riding my 4 wheeler.
Thats what you get when you leave the keys in the ignition. Deer will steal your ride every time.
Finding a gun thats good for everything from squirrels to deer is gonna be tough. I like the idea the other poster gave of carrying a handgun and a rifle. Deer season carry the rifle and a handgun for small game. Small game hunting, carry a 22 with a large bore handgun you shoot really well.
But if I am deer hunting I don't want to make any extra noise that might spook off deer. So a light weight rifle is what I will be toting. The squirrels and coyotes are safe for the time being.