My son's main piece of advice to my husband regarding our upcoming cruise is: if someone asks for your cruise card, it means your are going to be charged for something - don't hand it out unless you know what your are paying for ...
My husband's joking response was: What if you met some sweet young thing you wanted to invite to the room ...
Son: Forget worrying about what the ship will charge you, when Mom finds out, you'll be lucky if you still own underwear...
Gotta love my "boys" ...