They probably want the experience of hands on shopping. This can be hit or miss depending on when you are chartering. I agree with storm jib. Heavy stuff and 24 hours worth of food. Coffee, milk, yogurt, etc. It never hurts to send guests to the store while you are finishing up last minute details. They might even volunteer to cook the food they purchased!

Our biggest argument was always over water. I did not want to have to lug gallons of water to the boat in a dinghy, captain did not want gallons and gallons tucked away all over the place.