Cushions

Or floats, or even fenders in extremis.
The gov has made the first two and two are cut out ready to sew. They have closed cell foam inside so won’t absorb water or go mouldy, however they are quite firm. Will be a lot more comfortable than the slatted seats on the boat. The tab with an eyelet is for a lanyard to clip onto the seats so they don’t end up overboard.