This might be a good treat for receptions held at night. Guests will get to bring home a quintessential late-night snack, and writing a sweet note like "S'more love" adds the perfect tie-in to your wedding.
You can find treat bags at craft stores and bargain stores like Walmart. If you want to buy them online, I found some selling on Amazon for $7 for 100 pieces and on Paper Mart for around $14 for 1,000 pieces. Customize them yourself with some pretty calligraphy.