Though it is not required to give your priest/deacon anything as a thank you for helping to prepare you for the sacrament of marriage, it can be a nice gesture to give him something for his efforts. If you feel that the priest/deacon has been helpful, it would be good to show that. It can be a gift or gift certificate or money. Remember that the church donation does not go to priest. That goes to the parish. Check with the parish for guidance.