The quantity of stuff being recommended here is way out of control. Less is more. If you're packing more than one modest-sized suitcase per person, you're too focused on "stuff" and not enough on the experience. The more you drag along, the more you have to care for, and the more likely you omit something actually important.
Assuming a warm-weather trip, here's what I'd pack for myself:
- One outfit for each park day: shorts/blouse ... or casual dress ... each day's entire outfit neatly folded /rolled up
- One comfortable traveling outfit for your trip back home ... might be yoga pants and a tee
- Two swimsuits and two cover-ups
- One pair of worn-in-walking shoes for the parks: I'd wear Keds with no socks, but you might prefer walking sandals
- One pair of comfortable flip-flops for pool /resort wear
- One lounging-in-room outfit: flannel PJ pants/tee ... something oversized and comfortable
- If any fancy evenings are planned, appropriate special outfits
- Appropriate small clothes and two nightgowns
- One hat, sunglasses
- Toiletries, medicines, first aid, sunscreen
- If you have small children, pool toys or other small toys for the trip or the room
- Small bag for the parks: cross-body bag or fanny pack ... this should also be your travel bag
- Tickets, if you've pre-purchased them ... which might mean Magic Bands
- Upload all travel documents to your phone
- Phone charger for the room ... plus a pocket charger for travel emergencies
- Cash money (including small bills for tips) plus any gift cards or credit cards you expect to need
- One small ziplock per person for keeping phones dry on wet rides
- Glow sticks or bracelets from the Dollar Store
- For each park day prepare an envelope ... on the outside, type out your park plans, including any meal confirmation #s and fast past times ... in the envelope, place the money for meals and other anticipated expenses ... finish it off with a few Neosporin-infused bandaids. This means that on Monday, you just take Monday's envelope, and you're set.
This should all easily fit into a rolling carry-on bag.