Oh man, people love to watch a taffy-pulling machine. Also, a cotton candy spinner. Candy + motion = an engaged audience.
At the California State Fair, Liberty Safes had a pretty boring product: gun safes. The eye-catching feature of their booth was a video screen with an intreguing, fun video of four guys with sledgehammers trying to bash and claw their way into one of the locked safes. It was great! Showing your product being manhandled probably isn't good for most products, but it worked well for safes.
It takes a strong will to resist the urge to spin the prize wheel. Even if the prizes are valueless, spinning the wheel is a reward onto itself, and people love to do it. The larger the wheel, the more attractive it is to a crowd. A variation is to customize a roulette wheel. Another variation is to invite attendees to shoot a Nerf gun at a target. Everyone loves shooting a Nerf gun at a target.
This doesn't apply to most industries, but two seperate sauce companies had set up a banquet table of their dips. To keep the feeding frenzy under tight control, they handed out single chips to visitors, and let them dip them into whatever interested them. Both vendors were surrounded by interested visitors. I realize this is very close to just handing out food samples, but there was something special about getting to choose your own dip that made it twice as compelling.
A presentation that involves food holds the attention of an audience like the dolphins at Sea World. If a guy with a headset and an amplified voice is preparing smoothies, the audience has an inkling they are going to get some of those smoothies.
I didn't stick around to see how the merchants fared, but I'm certain the ones that made sales are the ones that drew attention.
If you are preparing to sell at a show, get something groundbreaking or get something traditional, but get something.