Get Ultimate Weapon for Tidus:
To get the Caladbolg, you need to have the celestial mirror. Once you have it, go race with the chocobo trainer in the Calm Lands. If you win the race, the person blocking the path in the north part of the Calm Lands will be gone. Then you can use the celstial mirror to get the Caladbolg.

Hidden Locations:
After u can control the airship go to the search option on it and type in the following:
X Coordinats/Y coordinates/Location
11-16/52-63/ Baaj Temple
12-16/41-45/ Sanubia Temple
29-32/41-45/Besiad Falls
33-36/55-60/ Mi'Ihen Ruins
39-43/56-60/ Battle Site
69-75/33-38/ Omega Ruins

Extra potions:
When you are on the first boat ride with Yuna and her friends, go below deck to where the seasick person is. There is a suitcase in the room.Kick it, and it will give you one potion at a time. It will give you up to 20 potions.

Overdrives:

Kimari: Use the Dragon Sword ability to drain HP and MP from the enemy. If the enemy has a Blue magic skill that Kimari can learn, he will gain it automatically. The only one that is difficult to get is "Sunshine", which you obtain from the Omega Weapon.

Auron: Find different Jeckt Spheres laying about the world. Some of these will give Auron a new Overdrive. You need to find all ten to get Auron's final overdrive.

Tidus: Just keep using them over and over. After a while, he will learn his next Overdrive.
Wakka: You can win new overdrive roulette (slots) types in the Blitzball Ranking and Tournament modes.

Lulu: Rotate the Right Analog-stick clockwise as fast as possible. The number will go up the more you rotate it. The more you level Lulu up, the easier it is to cast multiple spells.

Rikku: Rikku's overdrive combines items to create special attacks and power-ups during battle. You have to choose any two items to combine. Note: Two of the same kind will work.