Display the world map and then travel to the left-most island. On this island are powerful monsters that can easily level up your characters after battles.

Get free Potions in 'Timber Town' by having Rinoa in your party then go to the bridge where you saw the guards. Keep returning until a man appears. Talk to him and then talk to him a second time to receive a potion. Leave the screen and return until he appears again and keep repeating this process until you have the desired amount of potions.

You can get any GF during Disc Four at Ultimecia's Castle If you missed any on your way through the game. When you have defeated Sphinxaur select to unlock the Draw ability and you'll then be able to draw the following GFs from the corresponding Bosses.

Unlock Alexander:
Draw from Catoblepas

Unlock Carbuncle:
Draw from Krysta

Unlock Cerberus :
Draw from Gargantua

Unlock Eden:
Draw from Tiamat

Unlock Leviathan:
Draw from Trauma

Unlock Pandemona:
Draw from Red Giant

Unlock Siren:
Draw from Tri-Point