Is a camera necessary? If you have to ask, then the answer is no. If photography was really important to you, you would already know whether you needed your camera or not. But dont forget your phone charger and cable.
If swimming isn't something you want to do, then don't bring the suit. But really, how much room does one suit take?
But DO bring a basic first aid kit, and OTC meds like anti nausea, anti diarrhea, antihistamine meds- you may have difficulty finding your usual meds once ashore, and they likely won't be in the ship shops.
Also bring all the sunscreen that you will need for the trip. It's ridiculously overpriced on the ship.