Generally, a party host should get between 1/4 to 1/3 of a pound of deli meat for each guest. For 100 people, this translates to between 25 and 33 pounds of cold cuts.
Although each guest can be expected to consume around 4 to 5 ounces of deli meat, there are various factors to consider when planning a party. For example, if the deli meat is intended to be served as an appetizer, it is important to take into account whether there will be other snacks available. If it is intended for sandwiches, however, it can be expected that each sandwich will require about 1/3 of a pound.
Additionally, there may be attendees who are vegetarian or vegan. If there is a considerable number of guests who don't eat meat, less will need to be purchased.
The time of day at which the party or event starts also matters. Guests may be inclined to eat more at dinnertime than at lunch. A buffet-style setup is generally the easiest way to serve a party with many attendees, and in general, starches, meats and fried foods are the most popular items. Party planning professionals and caterers always err on the side of having too much food rather than too little.