Today they are defined in code, which I feel is maybe not the best way?
Loot box fixed in https://hub.darcs.net/ThomasLocke/godot-playground/patch/70fc2a5a97eebecd755b7d7daa2d8ded8aac335e
Bomb fixed in https://hub.darcs.net/ThomasLocke/godot-playground/patch/1992e541d90a522e11a5a705da9a98c2b7502681