That whole thing about twinkies having a really long shelf life is a complete myth. I saw something a while back on the history or discovery channel that talked about it. I think the myth got started since twinkies lasted longer than most other baked goods at the time they were created since they don't have any dairy ingredients. I'd say any canned foods or properly stored dry foods or even other candy bars would last much longer.

And aside from the high sugar content, I think twinkies have partially hydrogentated oil, making them very unhealthy, especially if consumed in large amounts as you would if you depended on them as a survival food. In fact if you ate only high sugar foods for any length of time you'd start feeling very unpleasant before long.