We overhead a company's sales representatives complaining about the fact that teachers grabbed so many of their specialty items. That's why you bring these items in the first place. Bring more than you think you'll need and distribute these items freely. That's their purpose. If you're worried about your budget, choose less expensive items.
Freebies make friends and that's more important than ever on today's crowded show floors.
Use your own products. There are instances when this is effective. If you have a low cost item that introduces a larger series, a sample from your product line or other products that are low cost but offer higher perceived value, they can be effective give-away's. Make friends with your local premium sales representatives. Get samples frequently and look at what other industries and market niches are doing.