Item Drops have several properties, some are only used by certain things such as the dungeon properties only being used by Dungeon JSON.
The id of the item such as minecraft:stone. Modded ids can be used and if nothing matches then this Item Drop is just ignored. Required.
The metadata of the item which is used for items or blocks that have multiple forms. Default 0
The minimum random stack size. Default 1
The maximum random stack size. If less than the minAmount, this value is ignored and the minimum amount is always dropped. Default 1
The chance of this Item Drop being dropped or placed in a loot chest, etc. Set to 1 for always and 0 to essentially disable this Item Drop without deleting it from json. Default 0 (never)
If set, the subspecies index of the mob such as 0 for normal, 1 or 2 for uncommon and 3 for rare. Note that creature json allows for the subspecies order to be changed. Default -1 (ignore subspecies)
An alternate item id to use when a burning creature drops this Item Drop. Used to drop cooked meat from burning animals, etc. Default: Empty
An alternate item metadata to use when a burning creature drops this Item Drop. Default: Empty