I found a bug where if you pick something up, then while it's in your face spam click on another item, it will give you that item without picking it up, as many times as you can click, for the short time the animation plays.
You can use this for ammo and coins but the two items have to be somewhat close to each other, because the pick up animation goes quick.
I think it does this because you can only pick up one item at a time, and you can't pick something else up till that item starts to go away. But since it's not fully away it won't let you actually pick up the next item you're trying to pick up. So it think you're picking it up but you're really not till the animation is over. So it give you the item as many times as you click it.