Final Fantasy Adventure

Final Fantasy Adventure is basically "Zelda meets Final Fantasy", and is the humble first game in the Mana series...back when Square still had some humble beginnings to speak of.

Unused Items
A total of 21 items are unused. At first glance, they are simply extra blank slots that never got implemented, but the Japanese version has unique names for each of these items.

They translate as the Flare Web, Flare Bazooka, Dummy Spare 2, Fire Ring, Rusted Key, Blue Orb, Red Orb, Mana Pendant, Mythril, Star Sapphire, Balancer, Moon Crystal, Scenario Spare 2, Scenario Spare 3, Scenario Spare 4, Scenario Spare 5, Torch, Dwarf Lamp, Earth Drum, Moogle Flute, and Reserve.

There doesn't appear to be anything associated with these items except the names in the final game. While some of these seem to be debug remnants, most of them may indicate that there would have been more story/key items at one point.

Regional Differences
The game was initially known as Seiken Densetsu: Final Fantasy Gaiden in Japan, with a North American release entitled Final Fantasy Adventure and a European release two years later called Mystic Quest (not to be confused with Mystic Quest Legend). One known graphical difference during gameplay is that the pentagram seen a few times in the game was replaced by another symbol outside Japan.