Yes. You can get 3 unique bonus items. They will be awarded for claiming your 3rd, 7th, and 14th prizes. You cannot get the bonus prize by only buying multiples of the same day prizes. While you can buy multiples at any time, to get the bonus prize, you will need to buy at least one of each day's prizes. For example, in order to get the day 7 bonus, you will need to collect each of the first 7 prizes of the first 7 days of the event.