Off the grid on Mackinaw Island

I’m roadtripping to Mackinaw Island, a notably low-tech place.  How good could internet coverage be on an island with no motorized vehicles?

We’ll Geocache our way there and back to add a little tech to the week. Storage-wise, the US Topographical map I’m using takes 3 gigabytes, and my Garmin eTrex Venture HC holds 24 megabytes. 

Talk to you in a week!