In order for a random item to drop as a death drop, it must be able to have been carried by the monster. This means that newts and such won’t get many death drops and the ones they do will be small.

Specifically, this approach doesn’t involve trying extra hard to pick an appropriately sized item, because then lightweight items such as scrolls and magic markers would become too common. It merely rolls up a random item, checks whether it would be the right weight for this monster, then decides not to drop it if it’s unrealistically heavy.