The trick to all of this is to pack efficiently and don't bring items that don't pack well. Well folded clothing fits better, and you should fold your dirty clothes as well, otherwise they take up much more space on the return.
For my next 7 day trip to WDW, I'm packing into a single carry-on sized bag, including a suit for V&A, and carrying on nothing but my camera bag for the parks for that day, and anticipate no issues and no laundry
Not WDW, but for a 16 night/15 day trip to Africa with several social events, where laundry is only available on Day 11 and onwards:
- Two pairs dress slacks
- Three pairs non-iron travel UPF slacks
- Four pairs utility/outdoor UPF pants
- Two dress shirts
- Six polos
- 5 T-shirts
- Four button-down UPF hiking shirts
- 15 pair underwear
- 16 pair socks
- 14 undershirts
- One pair boots
- One pair casual shoes
- One pair dress shoes
- One pair trail shoes
- Three belts (brown casual, black casual, brown dress)
- Fleece pullover
- Rain jacket
- Rain/trail hat
All but what I'm wearing (which will be the trail shoes, not the boots) fits in a single 24" checked bag that would be allowed as carry-on on Southwest.
And that's not counting the laptop, binoculars, three cameras, five lenses, three cell phones, headphones, et cetera, which fill up my carry-on bag. My remaining checked baggage allowance is being filled with maple syrup.