If you want to take your student out, explain where you are going and how much it will cost. Your student then has the opportunity to decide whether or not to go with you. Do not expect your student to pay for other members of the family. Many hosts are happy to include Under 18's as part of the cost of family outings.
However, please note that, if you are going out to dinner, meals are included in the student's rental, so you will need to pay for the student's meal.