Usually there is a large crew mess on board where it is possible to get something to eat or drink practically all day. The staff mess is smaller and quieter, usually reserved for concessionaires and their staff.
Don´t expect gourmet menus, food is presented in the style of a canteen, but you will not go hungry. Everyday there is a selection of meat, fish, vegetables, salads and desserts. If you are still hungry, the toaster is always available.