Items found at Duneman Isle: God Father, Kingly Armor, Yamoto Sword
By all means, have one of your characters equipped with the Trader Card; You'll randomly fight the Dragon, but he's quite different from his previous versions...not only he gives 30500 exp to each character, you'll get some of the best equipments and weapons from him. Defeating him isn't that easy, though; Bring Citan and Emeralda and equip everyone with Speed Shoes, then Fei should use Kokei or Yamikei with a Power Crisis (meaning it's ok to let him die and ressurect him with low HP; Fei'll take more damage that way). Using Elementals Deathblows with the other 2 is too risky, since they sometimes heal the Dragon. Note that you have to hover near the water to land at Duneman's Isle and you can't use gears here. Head to a desert island between Merkava and Bart's Hideout (You can see some kind of ruins on the island). After entering, refuse the Dune Men's offer and defeat them. Head closer to the sandfalls, and from this position, head East 3 times to find a regular desert area, then turn North. Fei will spot Sand Sharks on the next area, then continue North to find a fossil.
Jump over the fossil to get a Yamato Sword, then head back South. Go West to reach the top of the top of the sandfall, but you'll be quickly dragged back down, so choose one chest to get: The Kingly Armor to the left or the Godfather to the right (There's a good chance you'll have to repeat the whole process again, except for checking the fossil). After falling, you'll fight as a regular enemy from now on (There's a good chance you already chance fought one). Just use your best ethers to take him down. Take your time trying to beat the Dragon, it's really worth getting his exp. and treasure. You can exit the Isle now (Just keep going back West on the sandfalls area; You might have to help a Dune Man riding a truck to exit the area)) if you want, and:
Visit the Lighthouse, if you haven't done it yet, or...
Go to the final dungeon, Deus.