It's a Mom's world in my home. DH gets to pick a few shirts. The kids pack a few items for the plane. I check their bags before we leave.
We try for 3 suitcases for 9 days, 4 people. We do laundry after 4 days of our vacation at the resort. So, we do 5 outfits, 2 bathing suits, 2 extra t-shirts & 2 extra socks, 2 pairs of sneakers (wear 1 pair), flip-flops, 1 light jacket (worn on the plane). No jeans, no sweatshirts.
I also pack 1/2 used shampoo's & conditioners, plastic bags for camera's when it rains, a roll of paper towels. When we leave, we ditch most of our toiletry products.
We carry the film, camera's, our glasses/contacts, money, keys, ID's, tickets, etc... on us in carry on items.
I also pack some extra plastic hangers (from store bought items during the year) in the outside pockets of the suitcases. They are great to hang clothes in the closets, saving some drawer space. The plastic hangers are also left in the closet when we leave.
In the past we have over packed - never wore some clothes, did not need the items. We do not over buy on WDW trinkets. We get Goofy taffy, the new beach towel designs,....our DS wants to get some CD's in the music store in DTD, our DD wants to buy some earrings. We collect a few popcorn tubs during our week. We clean out the popcorn containers, fill up with socks, and pack them back into the suitcase.
Summer clothes take up much less space than winter clothes.
And if my teen DD packed - she would take up 3 suit cases of her own - I have to limit the queen of wardrobe to 5 favorite outfits (I do allow one sun dress and maybe 3 bathing suits for her).
So for our famly - 3 suitcases as checked luggage. DS & DD each have a small bag as carry on. I (DW), have a fanny pack and carry on (I have the sunglasses, hats,essentials) and DH has his camera bag as carryon.