LogFAQs > #909183951

There's an insane amount to keep your eyes out for honestly.

For reference: https://gamefaqs.gamespot.com/snes/554041-final-fantasy-iii/faqs/58436

The main thing, however, is when you finish the Floating Continent. Wait until the coutdown hits 1 second (IIRC) before you jump.

Some treasure chests change their contents (often to better stuff) after certain points (sometimes more than once). There's a guide for that too: https://gamefaqs.gamespot.com/snes/554041-final-fantasy-iii/faqs/40362

Many Rages are missable, especially early on. Try to get them all in each area before moving on (they're listed in the second part of the first guide above). One of Mog's Dances is also missable (fight a battle with them in the Lete River / Serpent Trench). I think some Lores are missable too.

I'm one of the few people that actually likes missables in games, including FFVI. They can of course frustrate you at times, but trying obtain as many as possible is a game in itself (and adds replay value). They're one of the reasons why the game has had such longevity for me, aside from it just being a great game.

Really though, you don't need to worry about any of this if you don't want. The game is easily beaten either way.