Answer:
It will keep moving at the same speed.
Explanation:
In space, there is vacuum which means that there is no air resistance. Since we remain in the state of free fall in the space, the impact of gravity is also negated on the friction. So the friction will be zero.
As per Newton's first law, we will need to apply external force to change the state of motion of a body. In this case when he let go of the lunch box it has a certain speed. This speed will not changes as there is no friction and no acceleration. So the box will keep on moving with the same speed.