This tool at kegulator.com is key for planning a any party. The site is simple and easy to use. Next party I have, I’ll be testing the Kegulator out. For 100 people it suggests 4 kegs, 120 cups and 177 pounds of ice.
What is really cool about the Kegulator is the sliders, which let you choose the degree to which your guest willl be drinking. Based on you estimates, the site adjust the amounts accordingly.