Paracord and Straps: Paracord can be used for a gazillion things and you can wear it as necklaces or bracelets for easy packing. And bring some straps for your hat, sunglasses, etc.
Medical Sea Pack: In case you get injured or must survive days away from a doctor, you'll want to pick up a mini medical kit. Again, one that is built for ocean survival.
Survival Tabs: Since space will be an issue, choose the tabs over ration packets. They pack the essential nutrition to keep you alive and going until rescued. To save even more space, pack them in a small baggie.