After thinking about a survival/hunting gun for a while, I have come to the conclusion that a 20ga shotgun would be the ultimate in versatility and usefulness. Shoot birdshot for rabbits, birds, squirrels etc...and slugs/buckshot for anything bigger. There's not much out there that can stand a 20ga slug to the chest. My friend has killed wild cattle with his 870 pictured above. The ability to change from shot to slugs means you can kill all size animals with it. I wouldn't really want to shoot a rabbit or bird with a 44 mag, although if it was a survival situation i would pick through the bushes to find all the small pieces of bird.
I live in Hawaii and deal with some of the wettest and most humid conditions around. I have a blued rifle and it does fine as long as you oil it after using. It'll go for a few days in the bush with just a little surface rust that comes off with the scratchy side of a sponge. Then I oil it and stuff it under my bed and there isn't any rust on there the next time I pull it out. If I am going on an extended backpacking trip I have a small piece of gun rag about 3"x3" that I keep in a ziplock saturated with gun oil. Then you can gurantee there wont be rust, and it hardly weighs anything.