Easy, I think you're right when it comes to a .22 as a good carry gun if your out in the boonies. It's not likely your gonna take the time to stalk big game if your in Fireman's "Survival" situation, and a .22 will take all the survival species (rabbit, chuck, squirrel, sittting bird) with apolmb. A couple of hundred .22 shells take up a lot less room then a similar amount of shotgun shells. But since this is an vehicle based discussion forum I think this whole thread applies to a "truck gun" and though mine is a shotgun, any firearm you are comfortable with, can take some abuse, and you can shot well is the right choice for you.
Another rifle that rides around in my truck a good bit of the time is an New England Arms single shot Sportster in .17 HMR. This gun is wicked on chucks, coyotes and squirrels, and is highly accurate.
If you truly find yourself in a true survival incident, you really should teach yourself how to set snares, make a frog and fish gig, and know how to hand pick fish. Then go out and put into practice before you need those skills. It ain't easy. And if you run out of shells for your survival gun or it malfunctions, that firearm ain't nothing but a club.