The bona fide battle kit contains:
• One boomerang
• One dragon scale
(These items can also be obtained by playing the game.
They can be obtained in both DRAGON QUEST I and II.
DRAGON QUEST I: Open the chest inside the inn in Tantegel.
DRAGON QUEST II: Open the chest inside the inn in Midenhall.)

More details on the official game page of Bona Fide Battle Kit ...