I carried a cedar train whistle with me along with a good call for years. Worked pretty well. I rarely use a shock caller any more other than an owl early in the day. Just don't want to carry them now.
Now for the goods. Probably 15 or 20 years ago I watched Uncle Ted Nugent turkey hunt on one of his shows. I believe it was in MI. Anyway, he had a big piece of sheet metal in his truck and shook it like crazy simulating thunder and got plenty of gobbles at first light. He called in a killed one of them on the show.
I carried a piece of roof tin in my truck for several seasons. Usually just used it preseason scouting but on occasion during season if they were quiet I would break it out. Got em started with it a couple times. I used a sheet that was maybe 3' x 4'. Not something you would want to carry.