It depends what your service centre require.
The standard requirement is to have the van in "as bought" condition, ie nothing inside it.
However some centres will allow some items to remain as long as they do not have to move anything to get to the parts of the van they need to, to carry out the service.
Also some insist that everything is removed to protect them from accusations of theft and accusations of items being damaged.
Anything you do leave will be at YOUR own risk.