Sea bags are not issued. It is personal preference on what they take. Keep in mind that they may have to do a lot of carrying between airports, hotels, and their ship(s). They will likely want to take their KP backpack with their laptop inside, so another sea bag they would want to carry on their shoulders is difficult. My DS took a seabag first sailing and decided on a wheeled suitcase second sailing. My DD took a wheeled suitcase, a small duffel, and her KP backpack on both sailings. They need to bring a lot of stuff, especially for second sailing. Also depends on the ship/route they have. If they are assigned to a tramp ship, they will not know their destination so they have to bring hot weather and cold weather gear. Cold weather routes require a lot of heavy jackets and insulated clothes which take up a lot of room. They also have to take stuff for sea projects, including a bulky sextant if a deckie. Your mid will have lots of advice from upperclassmen and sea year lectures. No need for you to worry (well, at least not until your mid is at sea and in 20 foot swells or headed for a hurricane...)