Treasure Chest (could be the "Odd Container" in your list):
In the Kelp Forest, on the same map with the small seperated section (where you get the 3rd cooking slot in), you have to swim to the left of that section (note that you have to be in the actual Kelp Forest and NOT in the seperated section, it's hard to describe) and then swim along the wall until you find a hidden cave with a wrecked ship in it. There you'll find a treasure chest.
Hilt of the Prince's Weapon:
Right after you got the Spirit form, swim down and then left past the hot streams.
Also, the Crab Armor gives increased defense. At least that's what Naija says.
Oh, and another one.
Mithalas Doll:
I can't exactly recall where, but I think close to the entrance of Mithalas (the city), you can enter a house that has nothing but a small passage that you can only pass in fish form. Do that, and you'll find a Mithalas plushie at the end. Since Mithalas doesn't have that many houses you can enter, it should be easy to find.
And yet another piece of info:
If you don't get the Arcane Poultice through the yellow fish thingy, there are about 4 in the last dungeon.
