He does look at things sometimes, but he can also be a thrower sometimes, so I only tend to give him things to play with on long journeys.
To be honest, giving him something to hold would make it worse as he is un clipping the belt to get out and reach things etc if he drops them. I also have a baby in a stage 0 carseat in the back too and if the baby cries/drops his dummy then DS1 is out and trying to help him. He isnt doing it to be naughty. He just see's things he want to get/do and forgets he isnt allowed to open the belt.
Is there nothing at all that they sell? Surely it is more safe to have something covering the clip than to have him bouncing around the car?