I'll assume you have an equipment setup, where you click on your inventory and it equips a weapon. If my assumption is correct, couldn't you script the items you want players to pick up just as if they were a weapon that goes into your characters equipment slot. Then for attacks you just script the base action out, toss, throw, swing, etc. Create a gui for when you run to the crate it offers ability to pick it up and equip. Now problems i can think off right off bat is the persistance of the object now being tied to player then not being tied to player. Would need to delete the instance on pick up and recreate it on toss.
Or another possible way would to make them stateful on pickup change state call a script to tie it to the players hand, on toss change state to being thrown, apply a FX to animate it, apply a damage value of it (perhaps from character stats) and check for it's collision with player, once fx is over, set state to normal, or blow it up or smash it whatever you want.
Personally I would think about treating them as weapons that can be equiped and thrown. Assuming you have the weapon swap on new item equip you instantly get position with bones worked out, animation with characters arm / movement, can easily treat it like a sword basically and give it abilities, apply player stats, keep track of it via your character movement etc, just like it was a weapon.
I'm sure there are otherways to approach it and some might be more effective and I just don't know it yet, still learning this engine, but have wrote games in several other engines, and that is the direction I usually take, as far as treating the items like weapons.