it really depends on what you mean by file types, if you mean your own extension... go ahead mak one up, rename all your file and associate the files with the application that would have opened the files before you renamed them all...
if you mean your own file types as in from scratch, then it really depends on what you are storing and how you want it stored...
plain text tables are the easiest thing to store, just choose text delimiters that can't be typed...