In order for items to be affected by gravity, they need to either have custom logic implemented or be RigidBodies. Save yourself the trouble and create Rigidbodies.
Now, if I understand this correctly, you need some sort of falling crates or packages that the player can collect. You can create RigidBodies and detect collision with the player by using signals. I guess your player character has an Area2D which is capable of detecting collisions with other Area nodes and RigidBody nodes. So, here's how to do this:
1) Go to your player's Area2D node and create a new script.
2) Then create an
body_entered() signal (from the panel on the right, under Node tab)
3) A new
func _on_Area2D_body_entered(body) function will appear in the Area node's script
4) Write the following code in order to have the collectible destroy itself everytime it touches the Area2D node:
if body.name=='<object's name>':
You can also create a variable which changes whenever a collectible is picked.
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