It's customary at most these events that guests bring some amount of $$ per head, this way they dont have to bring anything....
However these are mostly school parties that i do, and when i invite a large crowd to the restaurant.
The fact that its your party doesnt mean you should bear the financial burden this may become.
Tell them to bring some $$ to the party and you will bring the refreshments.
Between my friends and i, its an understanding. I'm not sure though how you would tell them to do so.
