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, there are a ton of affordable options on Amazon, like these Flat Glassine Wax Paper Sandwich Bags ($7 for 100). Customize them yourself with some pretty calligraphy.