Is there a word for something that you put on a fire?

Have you considered a modifier for "objects"? Perhaps "sacred objects," "beloved objects," "objects that would get him executed in some parts of the world," "objects that [insert nationality] would fight for," "treasured objects."

Fuel is typically something that you burn in a fire in order to extract energy (heat) from it. Adding fuel to a fire is a common phrase. (Incidentally, the idiomatic expression add fuel to the fire means to "make a bad situation worse", assuming that a fire bad because it is destructive.) A book may not be intended as a source of energy in this case by the burner, but it still works like fuel, so I think the word can still be used.

How about burnable.

Consisting or made of material that is able to be burned or is suitable for burning:

‘It consumed everything that was burnable, leaving behind only molten metal and frames of vehicles.’

‘People put out their trash, always conscientiously divided into burnable and not burnable, in an orderly way at the points indicated on the streets.’ (Oxford Living Dictionaries)