If you fly
My daughter's friend flew last week and had to dispose of an expensive face wash product because she had it in her carry-on bag and it was more than 3 ounces.
My husband went online recently to check the size limitation for carry-on bags and that's when he noticed that extra batteries must be stored in your carry-on bag, not your suitcase. We already had them in the suitcase.
Also be aware of weight limitations on luggage. On our trip last December, my daughter's suitcase was a whopping 48 pounds, just 2 pounds away from the limit. If it would have went over, they would have charged her $25.
There's also always the confusion regarding the "one carry-on bag" you are permitted to take.
For this trip, we've been trying to figure out who will carry on the laptop. After visiting the website, we learned that each person is allowed one personal item and one carry-on. Since the girls and I will each have a purse plus a carry-on bag, my husband can bring the laptop as his personal item.
Then there's the issue of a one suitcase limit for each person. Many airlines limit you to one and charge you for any additional.
This shouldn't be too much of an issue since it's summer and we won't be taking sweatshirts, jeans and bulky clothing. However (and I keep reminding my children), there will be purchases there that have to be brought home. My plan is to take a fold-up type of bag in my suitcase. If we need an extra bag for the flight home, I don't mind paying $25 for an extra piece of luggage going one way.
Another option is to ship items back home from Disney. I know the service is available, but I've never had to use it.
We always pack on the light side and do a load or two of laundry midway through our trip. It allows more space in our suitcases for things that we buy while we're there.