You might want to buy an aquabag for you phone / vhf / etrex.
If you are going boating in a SIB, expect to get damp, if not wet!None of these above are completely waterproof, unfortunately that include aquabags also, but they help.
Before anyone says the etrex is waterproof, its more wash basin or puddle proof. My second one is still alive, but it did needed a vacation to the airing cupboard after 3 months in the the rain on expedition. That said, I'm very happy its back, its a good bit of kit on land or at sea!
You can fit an anchor fuel and tool / flare box in your little (3.10m) sib, you will need the weight at the front (tied in) if its rough!