The phrase "door prizes" refers to gifts or items that are given to people attending an event or a gathering. These prizes are usually provided to attendees upon entering the venue through the door. Full definition
Contact local businesses to provide refreshments or door prizes for attendees. (educationviews.org)
Also, remember to bring your business cards to enter our draw for your chance to win great door prizes! (remonline.com)
Another tip is to offer some sort of door prize or giveaway to those visiting your blog — it can help get them connected with you and your blog. (5minutesformom.com)