We are having a graduation get together at a resturant mostly for family for our son. We are providing the cake & ice cream. But the guests will be responsible for there own meals how would I tactfully put that on the invitation?
Interesting question. I am not certain there is a tactful way of asking your dinner guests to pay for their own meal unless you reveal this at the time of the invitation.
Tell each family member and close friend personally that you would love to have them help celebrate this wonderful occasion but your budget won't allow for a dinner party this size. Ask each if they would be comfortable joining the party for ice cream and cake, while paying for their own dinner. Give the option to each that they can join in the dessert without coming to dinner if they wish.
You want to avoid giving the impression that dessert is the reward for paying their own way. Asking guests to help pay for your son's graduation party via a written invitation is poor manners.
I hope this helps and that you can arrange the celebration in a way that allows your son to enjoy the happy occasion.