Competitions, giveaways and anything interactive work well. Also something which you might not expect to see in that environment. I borrowed an F1 car once for an event based on a film franchise which provided additional relevant content and got a lot of attention. It stood out amongst the costumes, scenery and collectables.
Also just having proactive, upbeat people on the front of your stand engaging with visitors as they pass can work really well. A simple "hello," "how's business?" "what are you here for today?" or "what's your biggest challenge at the moment?" can be all you need to get people on to your stand and they should then be doing much of the talking. People are often very passionate about their business/organisation so being listened to can actually be a powerful sales tool.