This is my idea of a basic packing list:
For boys/men:
One t-shirt for each day of the trip
One pair of long jeans
Two pairs of shorts that match the shirts
Two long sleeve shirts
One hooded sweatshirt
One nice outfit for dress up night on the cruise
Socks/unders for each day plus an extra just in case
One PJ
Two bathing suits
(Remember you'll also have the clothes you traveled in)
One pair of water shoes/flip flops/crocs
One spare pair of shoes - maybe for dress up night, or just nicer sneakers
For Girls/women:
Same as above, maybe add sundress for casual, besides dressy outfit. Or capri pants instead of / in addition to shorts.
Don't pack too much - if you need to, you can do a wash.
Girls also like "princess" costumes, if you have.
Then, of course, all meds, toilettries. Don't need to pack shampoo or conditioner or body soap.
Sunscreen.
Batteries and chargers.
Some quiet time activities.
And most of all, don't worry - whatever you don't have, you probably don't need, or you can buy!
ENJOY!