It's daunting calculating food quantities for a 50-person barbecue. Running out of hamburgers and hot dogs would be embarrassing, but it's a waste of food and money to overbuy. Start with some basic math, but also consider individual factors. For example, how many children are coming? They'll do a number on the cookies, but probably won't touch the salad. How many sides and desserts will you have? How substantial are the extras? For how long do you have to keep everyone satisfied?
A standard rule for hotdogs and hamburgers is one of each per person. Since packs of burgers, dogs and buns commonly contain eight pieces, buy seven packages of each. Or, save a little money by buying bulk packages, which are typically twice the size; three bulk packages and one standard of each is adequate. If you're having a vegetarian barbecue, buy the same for veggie burgers and dogs. Count on using 8 ounces of boneless meats, such as steak, per person, so buy about 25 pounds. Add about 10 pounds to that if you're buying meat with some bones, like pork chops, and double the purchase if you're using meat with a lot of bones, such as spareribs.
Barbecues typically include a few kinds of chips and dip and maybe some snacks, like pretzels. Fifteen to 20 large bags of chips easily cover 50 people; 5 pints of dip should be sufficient. Pick up a few kinds of dip so there's something for everyone's taste. If you're putting out fruit or veggie platters at your barbecue, go with 5 pounds for 50 people. As for tossed salad, serve roughly one large handful per person, and don't forget to offer a few types of dressing. If you have a mayonnaise-based salad or two, such as potato salad, egg salad or pasta salad, buy 2 ounces per person, so pick up about 7 pounds of one type or 4 pounds each of two different ones.
If you're serving pie or cake, plan on having one slice per person. Offer about 150 cookies or smaller desserts so everyone can have three. If you're throwing in larger items like doughnuts or eclairs, one per person is adequate. Five pounds of ice cream is enough for 50 people. If you're serving a variety of desserts, there's no need to buy this much of multiple types.
A 2-liter bottle of soda serves 10 cups. Assuming your barbecue isn't an all-day affair, provide three cups of soda per person, or 15 bottles of soda. Reduce this if you expect a good number of people to be having alcoholic beverages instead. A 750-milliliter bottle of wine pours five average-size glasses, while the same size bottle of spirits pours 17 standard servings of 1 1/2 ounces. Buy three bottles of mixer per bottle of spirits. It's standard to provide three bottles of beer per guest if that's the primary beverage, which comes to 25 six-packs. Alcohol needs vary greatly from party to party, so consider its length and the drinking habits of your guests. Buy 100 pounds of ice, or a little more if it's going to be really hot at your barbecue.
Buy things you can easily pack up for guests to take home or that hold up well to have as leftovers over the next day or two. Things that get soggy or that don't reheat well are best avoided or should be purchased with a conservative estimate. Stock your freezer with a few hors d'oeuvres you can pop in the oven if it looks like you might be running low on food; if you don't need them, they'll keep. Guests are usually happy to bring something to eat or drink, which helps keep your costs down and allows you to have some extra food on hand and to offer a nice variety of stuff. Buy at least 100 plates, 100 cups and 200 paper napkins.