The three foods in a traditional campfire s'more are a roasted Jet-Puffed marshmallow, a HoneyMaid graham cracker broken in half, and three rectangles of slightly melted Hershey's chocolate.
Fish is an excellent source, with the highest concentration existing in herring, sardines, and salmon. Additionally, perilla, Chia seed, and flax have very high concentrations of omega-3.