check your math... 2 cups/per person * 30 people = 60 cups 60cups divided by 16cups/gallon = 3.75gallons You are going to need a very big pot for this. A 14" deep dutch oven only holds about 10 quarts and a 16" dutch oven holds 12 quarts.
I think 2 cups per person is going to be a bit shy. i would check over on the forums at the international dutch oven society www.idos.org
for recipes and suggested quantities. There are lot of scouters over there so you should get help. Cup for cup you will feed more people with chili then with stew (just a thought).
I would also recommend doing a couple of dutch ovens full of rolls. Get the cheap tube bisquits (generic pillsbury) and load a dutch oven full of them by laying them on their side in concentric circles and stack them on top of each other if needed. You can get about 60 in a 12" oven. Brush the tops with butter and cook them up at about 350deg. It comes out like a large loaf of bread that separates into dinner rolls. Warm rolls and stew....mmmmm.
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