How to cross a river while keeping kit (such as laptop) dry

Question

I am in the Balkans and have befriended a refugee who intends to crossing a river as part of their route. They are a very strong swimmer, having practiced it at a competitive level. They want to take their possessions across ideally without these getting wet. I am thinking they might be able to 1) tie a long piece of string to a tree on the near bank, 2) swim across with the loose end, 3) find a rock which fits well in their hand, tie the loose end to it, and throw it over a branch 4) tie the loose end to a tree, 5) swim back across, 6) untie the string at the near bank, 7) clip a waterproof bag such as http://www.iglusport.si/oprema/nahrbtniki-in-torbe/vodotesne-torbe around the string 8) tie a second piece of strong to the bag as a leash 9) tie the first piece of string to another rock, 10) throw it over another branch, 11) tie the first piece of string to a tree, so that it is as taut as possible over the river, 12) pull the waterproof bag with laptop etc inside across the river using the leash.

Is there a better method? I am aware you can keep valuables such as laptops in these bags (as long as you don't submerge them), but I thought suspending it across the river might provide a failsafe.

Answer 1

Keeping everything out of the water is of course the ideal answer, but a standard plastic waste sack is usually waterproof for long enough if suitably sealed, the "dry bag" types you've linked are sometimes not as water resistant but they are easier to manage.

As long as there's a suitable external container to stop the bags being damaged, a couple of layers of "black sack" with knotted tops will be plenty to waterproof anything for your purposes.