Every day you can select a random reward to add to the Delivery Truck. You'll receive the awards at the end of the week, but only if you're logged on at the time, so keep a watch on that counter!
Did you miss the delivery? You'll still have the option to use gems to collect your rewards for up to 5 days following the Delivery date.
Coins, gems, boosts, and even free play time can be rewarded through the Delivery Truck.