I always did this when riding to the Island, it meant I could have an enjoyable ride (via the backroads) to/from the ferry un-encumbered by luggage - now have a campervan, so no need.

I used to use a courier to send it to the hotel and dropped it off at the post office before heading for the ferry

You need to check Post Office opening/ferry times align!

Link here to parcel comparison site: http://www.myparceldelivery.com/