Let your exhibitors scan visiting users on their stands or use it as a seperate checkin to different areas to see how many that was attending the different sessions. Build competitions on which stand had most visits and which user visited most stands. You can even use it as a self checkin on a geo quest.

You can add a digital treasure hunt where questions and answers can be based on number combinations from different physical locations, photos, etc. For example, a task would be to find a familiar place, where you will enter the number on the entrance to the dental office in the first etage.