There is the old adage that does ring true: "Take half the clothes and twice the money."
Over packing is one of the biggest problems for first or sixth time cruisers. Often you will take too much stuff and never use it.
All you have to have is:
1. Boarding pass.
2. Passport or Birth Certificate with government issued ID
3. Credit Card with a good available balance.
5. Medications. If needed.
Anything after that isn't a requirement but just something that's nice to have.
Take care and enjoy.