If you are on the boat from Grand Portage, couldn't you leave a bag at the camp store at Windigo, for a fee, when you stop there? (Although in the period of time the boat stops at Windigo, I am not sure there would be time to run up and leave it.)

We were taking the boat back to Grand Portage on Thursday, August 25, and it turned around right before heading into the main part of the lake -- the waves were just too high. When we returned to Windigo, we were told that they would continue to survey the situation and we'd go back out if we could ...