Personal Items with ID that float would be the only definitive proof.
Perhaps there should be a re-write of international standards for things like passports and credit cards and boarding passes, that requires them all to made of some laminated plastic material with tiny cells within them, such that they would be able to float in water.
Perhaps there should be a re-write of international standards for things like passports and credit cards and boarding passes, that requires them all to made of some laminated plastic material with tiny cells within them, such that they would be able to float in water.