It's National S'mores Day! No simple snack can seem quite as much like a summertime staple like the S'more, and there's no better day to celebrate the gooey and delicious treat like on National S'Mores Day! The August 10 celebration of the classic summer campfire snack, which is rumored to have gotten its start with the Girl Scouts back in the 1920s, is also a perfect day to kick back and enjoy one.