When you have a large crowd to feed, potatoes are your friend. They're inexpensive and filling, and can be served as either a side dish or a light meal in their own right. With some advance planning, even a single domestic oven can turn out enough potatoes to feed a large crowd. Use medium-sized bakers as a side dish, or large potatoes if baked potatoes and toppings will form the entire meal.
Scrub your potatoes under cold running water with a stiff brush, removing any surface soil, eyes or blemishes. Dry the potatoes with paper towels.
Sort your potatoes onto baking sheets by size. A home oven won't fit a commercial-sized sheet pan, but a 3/4 sized sheet -- 15 inches by 21 inches -- will work. This size sheet can hold 20 to 24 mid-sized potatoes, or half that number of large potatoes. If the potatoes on each sheet are all approximately the same size and shape, they'll be easier to manage.
Pierce each potato several times with a fork, paring knife or bamboo skewer. This lets steam release as they bake, and prevents the potatoes from exploding. Rub or spray the potatoes lightly with cooking oil, and salt the outsides with a light sprinkling of coarse salt if you wish.
Arrange your oven with two to three racks, spaced to permit the same number of sheets of potatoes. Preheat the oven to 400 degrees Fahrenheit.
Bake the potatoes for approximately 1 to 1 1/2 hours, depending on size, rotating the sheets every 30 minutes so they bake evenly. The potatoes are done if they're tender when pierced with a bamboo skewer, or when their internal temperature reaches 205 F to 210 F when tested with an instant-read thermometer. Serve the potatoes immediately, or cover them and keep them warm for up to an hour.
Count out the number of potatoes you need. Purchase or borrow enough picnic coolers to fit the entire quantity of potatoes.
Scrub the potatoes with a stiff brush under cold running water, than pat them dry. Arrange the potatoes loosely on your baking sheets, grouping them so that each sheet contains potatoes of roughly the same shape and size. Pierce them in several places with a fork or bamboo skewer.
Preheat your oven to its highest temperature, usually 500 F, and bake the potatoes at that temperature for 30 minutes. While they're in the oven, fill your picnic cooler with hot water. Just before the potatoes are due to come out, drain and dry the cooler.
Transfer the hot potatoes to the cooler, and close the lid tightly. Fill the oven with a fresh batch of potatoes, baking them for 30 minutes as well. When they're done, add them to the cooler on top of your previous batch of potatoes.
Repeat until you've baked all of your potatoes, preheating and filling new picnic coolers as necessary. The potatoes will need 45 to 60 minutes in the cooler to finish cooking, depending on their size, and can stay warm for up to six hours if they're unopened.