Even though the on-board laundry services might tempting, these services can really add up, especially laundry, as charges are per item and the rates are similar to those charged in hotels. If doing laundry is important to you and you don't want to send it out to be done, look for a cruise ship that features a low-cost or complimentary self-serve laundry room (they usually feature an iron and ironing board in addition to washer and dryer).
An alternative is to hand wash laundry and hang it to dry in your bathroom. Tuck a small bottle of laundry liquid and clothes pins in your suitcase. Don't bring along a travel iron to touch up wrinkled garments! Irons are a fire hazard. Instead, pack a clothing steamer or hang wrinkled items on the bathroom door while you take a steamy shower. Wrinkles should fall out.
What do you do with the dirty clothes you amass while on board? Consider bringing a foldable hamper. You can usually get them at the dollar store. They fold flat in your suitcase and if you don't want to bring them home leave them. After all, they only cost a dollar.
A possible alternative to taking a hamper for dirty clothes is to take along a couple of kitchen size plastic trash bags (the kind with the built-in drawstring). You can hang the bag on the metal bar inside the closet on and you can toss your dirty clothes in it each day. On the last night, squish the air out of the bags and put them into the suitcases first, which kept the dirty stuff separate from everything else. At home, toss the bags into the laundry room.
On cruises, there are plenty of freebies to be had. The secret is knowing where to find them!