We used to pick names out of a hat on Thanksgiving. We were the Kriss Kringle to whomever we picked, and this meant praying for and being especially nice to that person throughout Advent so that, hopefully, by Christmas, he or she could guess you were their Kriss Kringle. In my family, each person would receive a gift from their Kriss Kringle on Christmas Eve. For us it was the first gift of Christmas, and we looked forward to coming home from the anticipated Mass, having dinner and opening our KK presents.
There are several variations to how this can be done, and many people call it Secret Santa.