Interesting. If you want it to reflect off objects you could set the velocity when it spawns, then put all the objects you want to reflect off in a tag and then use the collided behaviour with the tag selected and either multiply the x velocity by -1 and set to that. Or use collided on left, set velocityX to positive value; collided on right, set velocityX to negative value.

How are you making your item box? Are you making it spawn an object? Maybe it's spawning it self and it's causing too many to spawn resulting in lag. Or maybe the graphics are too large. More details on how your project is created would help.