"As for Milk cartons, they work till the boat fills with water, then
they
give up on life and either pop the lids off or go wondering down
stream."

Is that from experience Mike ???
I've tried popping the top off an empty milk carton by applying sudden
pressure, and they don't fly off. + placed all together in a net,
there's no way they'll ever get out, as they are larger than the gap
when my back rest is in place (again the old physics thing kicks in
!!!).
I'm interested if you've tried this and it's been unsuccessfull.
MB