You should make a list of things you will bring on your sailing vacation. This will make it easier for you to pack only the essentials even if you will only be away for a few days.
The first thing you have to get is a bag. You must never use hard sided suitcases because of the limited space. Instead, use a duffel bag or back pack. The nice thing about them is that they can be folded when you have transferred your clothes into the closet.