I massively overpack for Disney. For a 4 night stay, just for me, I have two luggage bags, a cooler, a camera bag, and a tote bag with food (I typically check 5 bags for myself if staying solo - if I go with a friend, I add in their luggage. I bring 10 pairs of shorts, 10 shirts, 4 sleep shorts, 12 pairs of socks, 12 underwear, 5 pairs of shoes, toiletries, 14 cans of soda/tea, 10 bottles of water, my camera bag has 6 lenses, I bring 3-4 books for reading, and various food items (DVC villa with full kitchen. Of course, the fact that I only drive 2 1/2 hours to Disney, and my car has no restrictions or limits on luggage...it's easier to just toss in far more than I need - the only downside is if staying in one of the resorts where you park by your building and bring everything in - there usually aren't luggage carts, so I have to make 2-3 trips back and forth from the car to bring everything in. But it pays off sometimes like when it rains 3 of the 4 days and I end up with soaked clothes - I can change 2-3 times a day every day and not worry about doing laundry.
And that's as a guy. One girlfriend that often likes to come will bring clothes for the parks, more dress-up clothes for evening, specialty dresses or clothes for parties or events, and far far too many shoes between the casual & dressy stuff. Hats, accessories, makeup, different handbags/purses for different outfits, and so on. I have to fold down the seats in my SUV and use the back seat with her two massive suitcases plus my 5 pieces. I've had Bell Services unpacking the car ask me how many weeks we're staying, and look at me a little funny when I say '4 nights'.
When I go with friends who live in Florida, they generally follow my lead and overpack as well. But when I travel with a friend from out of town who had to fly down to stay with me, they look positively spartan by comparison with their 1 little bag with just enough clothes to cover 5 days.