I always do laundry during our stay because I prefer to pack a bit less (and there is usually an afternoon when the kids need down time and I'm too hyped up on chocolate-dipped Mickey-shaped Rice Krispie treats!)
I have a few suggestions for you, either way:
Bring a Shout stain stick in case someone gets a spill (if the garment sits in the laundry bag for a few days it will be even more likely to stain).
Buy your laundry detergent and dryer sheets before you leave home.
Target sells travel-size (4 loads worth) of liquid Tide and travel size Bounce sheets. These are sometimes sold at the Dollar Store, too.
I made a mistake of forgetting the laundry supplies on our last trip. I bought some detergent and bounce in the store on the 4th floor of the CR. It was expensive-- but I had to have it, right? Then I went over to the laundry room in the South Wing and saw the same supplies for 50 cents less in the vending machine. LOL I felt like a chump.
Doing laundry at the resorts isn't bad. I have had only one negative experience with some pushy grumps at the Poly (they were taking people's stuff out and dumping the wet clothes everywhere). I never leave my clothes in the machines anyway but witnessing that clinched it for me. In general, people have been super nice and even donating leftover laundry supplies to people who may need some.
