Certain items like Holy War in FFVIII i definately save to the end.

But if it's a game where I know what the final boss is gonna be like, I've learned to use them when I need them. in alot of the FF's you're not going to need to use most of the elixers/mega/x/whatever in the final fight so I use them when its appropriate. Although its real fun in games like VI, checking every clock to build up your elixers throughout the entire game...only to find the final boss is a piece of cake if you've been searching thoroughly, anyway.