Not all weddings are high dollar events. Whatever demographic you're shooting for, you should have appropriate print materials and sound/video samples. If you're going for high-end weddings, you should absolutely have professional materials to hand out. If you're a "typical bar band" that is looking to play some weddings too (presumably at a lower than "A-level wedding band" fee), I think it's OK to have DIY materials, as long as they are put together with some thought and care. In addition to song lists, gear, gig dates (where they can check you out) etc., you might have a sample contract to show people that you'll have all of the bases covered for their wedding. Look professional at all times. Dress appropriately. Get rid of the stupid table in the booth if the venue provides one (or place it in the BACK of the booth) -- nothing worse than a couple schlubs sitting behind a table looking bored. If you can stand for a 4-hour gig, you can stand at a wedding fair. Absolutely no food in the booth.
I've worked a lot of tradeshows, and the biggest thing I've learned is don't wait for people to come to you. Know in advance who will be exhibiting and seek them out -- wedding planners, venues, even DJs (maybe they have customers that are interested in a DJ and a band?) Work the room and gather leads. Have a way to capture leads (brides-to-be) at your booth so you can follow up immediately after the show. Set up an account on ConstantContact, and figure out how to let your leads submit their contact info (bring a laptop to the fair) -- it's pretty easy. Take notes about the lead's specific questions and concerns so you'll be prepared when you follow up with them.
I'm not crazy about the 10% off stuff. It seems a little desperate and superficial. Depending on what kind of gear you have, maybe you can offer something like a free upgrade to your deluxe fancy-schmancy lighting rig, etc. Don't expect anybody to book at the show. Extend the offer to anyone who signs your registry. Save the cash discount in case you need it to close the deal later on.
Lastly, consider doing something out of the box. Have a guitar or two hanging around and use it for pictures. Make the bride-to-be a rockstar. Better yet, bring a freakin' drum kit too and snap pics of the bride-to-be on the throne. Post everything to Facebook. Make her remember you.