While you won't get the best popcorn ever, nor the ease of the microwave
...one thing you can do is cook it over the fire in tinfoil. My little Cub Scout Pack loves this one. Get a square piece of tin foil and pour a table spoon of oil in the center. Drop some popcorn in the oil. You want all of the kernels to get covered with oil. Add some salt. Fold up the sides of the tin foil to make a "tent" around the corn. Attach the tent to a string, string to a stick. It will look like you've been fishing and caught a tin foil fish. Hold it over an open fire. Be patient, don't rush it, or you'll have burnt corn. Also take care not to burn your string or the whole thing drops into the fire...back at square one. It's a fun alternative to roasting marshmallows!