Not surprisingly, there isn't a huge amount of choice in the waterproof swimming rucksack market - but there are a few models available. Will has gone for the OverBoard waterproof backpack. He likes his rucksacks like he likes his men - big, strong and black. At 60 litres he should be able to swim with all his camping equipment on his back, as well as his running kit, wife and kids.
Full kit report once they've actually been delivered and we've had a chance to test them.