ItemToss

The ItemToss Event is fired whenever an Item is being tossed from a player’s inventory.
Canceling this event will prevent the item from entering the world, thus causing the item to be deleted.

Event Class

You will need to cast the event in the function header as this class:
crafttweaker.event.ItemTossEvent
You can, of course, also import the class before and use that name then.

Event interface extensions

PlayerDeathDrops Events implement the following interfaces and are able to call all of their methods/getters/setters as well:

ZenGetter/ZenSetter

ZenGetter Type
item IEntityItem
player IPlayer