Well if your on disk 4 then you've already missed heaps of side quests(Mr Morrids coffie,Burmecian children,+ others).Have you done the choco side quest yet? You need to do this to get to half the other ones any way. If youre up to memoria then you can also fight Hades and gain acess to the legendary synthesis shop.You can find this guy in the screen before the Kraken fight. Then theres also the zodiac coins......