I heard that some food materials can be kept for a long time if they are sealed in a vacuum box and kept under the water. Which type of food stuffs fall in to this category and whether is it useful to follow this method.

I wouldn't recommend this method at all. If your vacuum integrity is lost, you just wasted perfectly good good. Usually, MYLAR bags with oxygen absorbers added, sealed in 5 gallon food storage containers, is preferred. Here is a YouTube video showing the basics of food storage:

http://www.youtube.com/watch?v=vW7_cTn6YpE