ok, i really dont consider myself an expert...(yeh i do, i know everything about final fantasy... heh)
heres how it works...
the items u need r the secret items from each temple every one is gotten by using a destruction sphere...
there r a few temples that u can not go back to, for obvioius reasons...
if u missed an item, sorry, but u do have to start again...
but, dont sweat it, once u done it once, it comes easy..

hope i helped...