umm users can drop items by clicking the 'Toss' button at inventory.php page. I have not coded a script to enable users to pick up dropped items, it should not be difficult to accomplish though since the idea should work out in a similar way as Pound script.
For now the only way to obtain items is through itemshop, but this will change in future. When a battle system is available in Mys v1.5.x, admins should be able to assign items dropped by enemies. I coded a quiz system for my Pokemansion site, in which users receive fishing rod by completing fishing quizzes.
So yeah, you can do whatever you want to extend the item/itemshop system with PHP programming.