No, not gift certificates or a chance to win a family pass to Wally World!
When someone walks into your open house today, they are looking for one thing: information. If they are a buyer, they are trying to find a home that fits their needs. If they are a seller, they are checking out comparable properties. If they are a perspective seller, they are checking out comparable properties and REALTORS®.
Give Valuable Information 
As an industry, we do a good job of disseminating information regarding our listings. We print up color fliers, we placed open house advertisements in the local paper, and we fill glossy color Homes magazines with images of the American dream. But what about all the people who walk into your open house today that determine the home does not match their needs (either as a comp or a destination)?
Try giving out valuable (yes, I said valuable) information at today's open house. An example would be a list of all the homes for sale within ¼ mile of your open house, along with their size and price. Or, try printing a list of all the open houses in your town today. Print this information on that back of your open house flier. Or, print the pricing curves for the town that I wrote about last week (see my blog on Fixers). Hand the flier to each visitor, give your 1-minute elevator speech about the home, and point out the information you've provided on the back. Now you've not only provided information about the home you have open, you've provided information about the market.
Mitch Todd/member of GreenerMarin at Keller Williams Realty in Marin

Mitch.. I give away lots of things.. including a copy of my newsletter and how to subscribe.