On Explorer there is a Cafe Promenade, which serves sandwiches, pizza, desserts, coffee. It's all free. There's also Johnny Rockets, but I can't remember if this in one of the ships that is going to start a surchage for eating there (which is a BAD move, in my opinion). In the royal promenade there is also a Sprinkles, which is soft ice cream - also free. And, of course, there is always room service.