Make a guess is one of the oldest activation concepts out there. If you have not heard about it, you have some catching up to do.
Here is how it work: Fill a jar with gumballs (or anything you like)
Take a photo and upload it to the system
Fill in how many gumballs the right answer is. Then ask your customer to make a guess of how many gumballs there are in the jar.
Once a person makes his or her guess the system will save their guess. When the competition is over the system can automatically announce the winner or you can simply check by yourself who had the closest answer. Send out a message to both the winner and everyone else to tell them if they won or not. Combine the activity with a digital coupon which enables the winner to collect the price in your store.