You shouldn't really need to eat on an 18 mile ride. I think a lot of people eat way more than they need to on the bike. Human beings have metabolisms, the ability to store energy and utilize energy as needed, we don't need to eat constantly on the bike.

With that being said, I personally drink my calories on a long ride. I use mostly protein shakes. Mine are carb free cuz I have impaired glucose tolerance but my husband uses a protein-carb drink that he likes a lot. I'll also snack on almonds as needed.