Any salesman will tell you that the best sales prospect is a referral - more sales are made from referrals than any other source and in terms of the volume and quality of sale, referrals are the undisputed number one resource. At the same time, most sales people don't ask for referrals and it is a case of, "If you don't ask, you don't get!"
At trade show events there are thousands of attendees wandering around the venue, and all of them are a potential goldmine of referrals for your business, and in terms of your specific trade show, for increasing visitor traffic to your booth.
Trade show promotional gifts, or giveaways, are typically poorly managed by exhibitors in that they are handed out freely, or left lying on a display for visitors to help themselves. Instead of just giving the free stuff away, try using gifts for rewarding visitor behavior, such as spreading the word about what is happening at your display or bringing colleagues and other guests to the display or a product presentation.
There are some general rules for you to follow when incentivizing attendees to go and promote your booth and trade show event presence:
Sales and booth staff should be trained in asking for referrals and how to ask for them - they should be instilled with the need to ask for referrals on every occasion, even with the same individual at subsequent meetings;
Be sociable and friendly - make a joke of what you are doing with the attendee because they will know why you are asking and what is happening, this is a normal course of doing business and a good salesman will always ask for referrals and the attendee will know this;
Let your products and service standards speak rather than promoting the features of the product offering itself - try asking an attendee this kind of question, "I can see you're interested in what we have here, if I give you this [promo gift], how many people will you bring to my presentation at 3pm this afternoon?";
Go for qualified quality not diluted quantity - remember we are trying to generate real interest and enthusiasm so don't simply go for filling your booth with bodies; it's better an attendee brings you one hot prospect than a dozen hungry mouths looking to eat your food, drink your good coffee and waste your valuable time; and
Ask your new visitors for referrals too - this is a reiterative process and every new contact is a new opportunity to make even more contacts!
Asking for referrals is the hallmark of well-trained sales professionals and not asking for referrals is going to be noticed by your prospects, especially if they have sales training themselves (and many will). When you are making the request for referrals, couch the request in terms of how happy the prospect has been with your presentation, product or service offering (this reinforces their idea about you too), and then explain why you are making the request. It becomes very hard for someone to avoid the referral request to help you, especially after they have agreed that you have a good product/service or a great presentation.