Cooking for a large group may seem a bit exasperating at the outset, but try not to focus on the number of people and instead concentrate on the amount of food that needs to be brought to the table. The amount people normally eat won't change just because they are in a group setting. Caterers tend to use weights when determining food amounts and don't spend as much time trying to figure out how many pieces of chicken or slices of meat they need. Their standards are usually spot-on and can save you a lot of time and headaches.
A standard portion of meat generally tops out at four ounces, or a quarter-pound. You can go higher if you like, but this is usually plenty. Using that number, you can serve four people with one pound of meat. Taking that further, you would need 10 pounds to serve 40 people. When serving meat to a large group, it's smart to concentrate on preparing roasts that you can slice, as opposed to cooking individual pieces of chicken or small steaks, which can get pricey and time-consuming. Serve dishes like roast beef, prime rib, baked ham or roast turkey.
Shop for roasts at three and four pounds or larger and combine them to reach the 10-pound mark. Take care when you are buying meat with the bone-in--the bone will be reflected in the total weight, so you will have to compensate. Also buy an extra couple of pounds of meat for surprise guests or hearty eaters.
Most people enjoy pasta, and it's a common choice for group meals because it's cheap and easy to prepare without much fuss. If you're buying regular spaghetti, stay with the rule of four ounces of dry pasta per person. You'll only need two ounces per person if you're buying macaroni. If you're using fresh pasta or a larger noodle like rigatoni, check the package and look at the recommended serving size to estimate the amount you need. If you are serving pasta as the main course, add one or two extra pounds of dry pasta to be safe.
The same weight rule generally applies for rice if you are using it as a side dish. You will need about four ounces of dry rice per person, or 10 pounds for 40 people.
Buy 10-15 pounds of vegetables for your group of 40.
If you purchase food at a warehouse store, you can find five-pound bags of pre-cut broccoli, cauliflower, carrots, green beans and many other prepared vegetables. Place these vegetables in a pot of salted, boiling water and cook them fairly quickly.
Potatoes are an excellent side dish because you can prepare them ahead of time and warm them up before service. You can parboil baby potatoes until they are fork-tender, drain them and put them in the refrigerator. Later, place them on a roasting sheet and bake for 20 to 30 minutes to warm them up. You can also prepare mashed potatoes ahead of time. These tend to be particularly good when twice-baked.