Tipping in Midway Islands is probably the last thing on your list of things to worry about. In fact, if you got to the island as a tourist you would have a story to tell! The island is owned by the US and is looked after by the U.S. Fish and Wildlife Service. It is now a protected island due to its fauna and small wildlife. You won’t be able to visit unless you are part of the military or a research group.
If you do get the opportunity to go the tipping wouldn’t be a concern! There isn’t any services on the island and it is uninhabited. Have fun though! Its a once in a life time experience!