Serve root beer floats and orange soda floats. You will need to have vanilla ice cream and orange sherbet delivered by one of the grocery delivery companies and two cases of root beer and one case of orange cream soda. Get a premium root beer and orange soda like Henry Weinhard's, boylands, or Stewarts.
There are several beverage centers that will delivery in Manhattan, like:
http://www.newyorkbeverage.com/delivery.html

Plastic cups, spoons, and straws and everyone will have a good time.