Mana Eggs
Equipping a Mana Egg will add a boost to certain types of Magic, causing spells of that type to do more damage or be more effective. In order to use a Mana Egg, a character must have a Magic Level equal to or greater than the Mana Egg's minimum required Magic Level. Magic can also be extracted from Mana Eggs at Magic Shops.

Skill Books
Equipping a Skill Book will add a boost to certain types of Skills, making them more effective. In order to use a Skill Book, a character must have a Skill Level equal to or greater than the Skill Book's minimum required Skill Level. Skills can also be extracted from Skill Books at Skill Shops.

Boost Effects
There are several levels of boost--the more powerful the Mana Egg or Skill Book is, the greater the bonus will give. You can check which boosts a character has on the Setup Screen or the Magic/Skill list screen. The red-to-yellow guage indicates the power of the boost.