We recommend that you bring a first aid kit and any medicines you may need. [the health system in Guinea-Bissau is precarious].
You should travel with a waterproof jacket (the sea can be rough) and that you bring amphibious shoes with good protection (there are rays all over the archipelago).
We suggest you should also bring repellent, sunscreen, a hat, a beach towel, pants and walking shoes (for visits to the villages), a water bottle, a flashlight and binoculars (for birdwatchers).