We always advise that all valuables stay locked away in your vehicles. Anything that can sink or can be damaged by seawater is best left on the land. We have somewhere for your keys (this will be explained in the briefing when we meet).
Waterproof cameras are welcome, we suggest that they have a float and lanyard to attach to you, so they don’t sink. Phones are best left on the land as they are difficult to attach to you and are rarely salt waterproof. If you do decide to take your phone with you please put it on aeroplane mode, so that you are not distracted from the safety instructions and for the enjoyment of others on the tour.
A bottle of water for rehydration is sometimes handy…if it is very hot a hat for paddle boarding can be nice too.