Place your fish filets in a bowl or ziplock bag and cover with buttermilk. Let sit while you shake together equal amounts flour and cornmeal (for 4-6 filets, start with about 1/2 cup each) and season with your choice of seasonings, salt and pepper.
In a heavy skillet on your camp stove or over an open fire, heat an inch or so of oil until it's hot, but not smoking. Pull each filet out of the buttermilk, let the excess drip off, and dredge in the cornmeal mixture to coat. Fry, turning with tongs, until golden brown.