I see good suggestions all around the lake, so it's not clear where OP's homeport is.
Lobster, clam chowder, corn on the cob.etc, etc. Not available in Seattle. outdoors, shorts and sneakers, almost anyplace.
Unique, New Hampshire? The Crystal Quail. An easy drive from Alton. A little more from other starting points. And have your friends enjoy the NH Wine and Liquor Outlets. Go to one of the wine specialty outlets for huge selection. (Yes, I'm "one of the owners") They'll have to buy the wine and bring it to the Crystal Quail. (No financial interest here.)
http://www.crystalquail.com/