I'd have to agree that if a .22 is really best for your circumstances, then an accurate rifle will always be the best bet. It should preferably be able to keep all its shots inside a 1/2" circle @ 25 yards with its favorite ammunition. Less accuracy will only limit you more. And as Mr. Mutt said, don't rely on an inaccurate rifle simply because it stores easily. And I'd also have to agree with his comments about bringing an accurate pistol rather than an inaccurate rifle if space is at a premium.
Chief AJ once told me Ruger's .22 auto pistols are usually more accurate than their 10/22 rifles from the factory. In the field you can use a sling or stick to help steady your aim and increase the pistol's effectiveness. You could even lash a stick with a crotch at one end directly to the barrel along the left side of the reciever like a stock for a steady aim. (note- it is illegal to attach a shoulder stock to a pistol, and I don't know if they consider a stick the same as a stock. Best to just keep this info in mind for a true survival situation)
Also, practice a lot with your chosen gun before you actually need to depend on it!
Now having said that, I don't personally believe a .22 will always be the best caliber for a survival gun. As mentioned, it is capable of killing bigger game with absolutely perfect placement under ideal conditions, but I sure don't want to handicap myself that badly, especially if I'm starving. It would be a piece of cake to drop a bigger bullet into the 8" kill zone of a deer facing you from 100 yards away, but with the .22, you go hungry. As I've said before, we seem to have more deer than small game in my area. The most squirrels I've seen on one outing this year was 5. In contrast, deer graze along the interstate in herds of over 100! Think about this- a rabbit has, what, about a pound of meat? Compared to upwards of 100 pounds on a deer. (here in the midwest) Think how much more smaller game you have to hunt (and how much more precious energy you must expend) to keep yourself fed. Do 100 rounds of .22lr
really take up less space than one larger round? A bigger bullet will kill small game too, ya know.
I'll just throw out one last idea here. If you're not sure whether you need a .22 or bigger gun, but space is at an absolute premium, why not consider the break action Contender or Encore pistols from Thompson Center? You can easily carry an additional barrel and swap them out in a matter of seconds. Even in serious calibers, I often see guys put 5 rounds into a 1/2" group @ 100 yards from a decent rest. Heck, you can even get a barrel chambered in .410 shotgun. They are available with shoulder stocks too, and break down quick & easy.
Myself, I like the idea of having a repeating rifle of decent power as well as an accurate .22 pistol, but if I had to leave one behind, I'd leave the .22.