Probably the most useless "gadget" was the Coleman Grill-Top Coffeemaker. If we wanted a cup tomorrow, that's fine, but good golly, it took way to long to make a pot of coffee. We went back to the old fashioned perk coffeepot.
We gave it to a friend as he'd been looking at them. I suspect it's still stored in his "items never to be seen again until his kids clean out the place" garage....