Welcome to SMF...
Your guest makeup comes in to play and the type of event. A mixed group of men, woman and kids? All adults? Mostly men? Furthermore, Guys at a Superbowl Party will eat more than folks at a Kids Birthday Party or a Ladies Luncheon.
In general having 2 meats, figure 4 people per Rack of ribs, 2 to 3 bones and 1/2 pound Chicken wings, 3 to 4 pieces. So, 15 racks and 30 pounds of wings...JJ