My friend, I live for this kind of question! Obsessive "light packer" here. I've packed carryon-only for 10 nights in Scotland in the fall (with laundry), and 7 nights in Scandinavia (sans laundry), in the dead of winter! 7 nights in Orlando is totally doable. In fact, nobody in my family has ever checked a bag since the kids were born (which is the result of a long story: suffice it to say, I used to travel for work frequently, and learned the pitfalls of checking luggage).
Here are my tips, in no particular order:
1 - Make a packing list ahead of time (I do this for each member of the family, and they're great about using them), edit it carefully, and stick to it ruthlessly. This is where your carry-on plan will be made or broken! There won't be room for last-minute "maybe I'll need this" items. It's a guarantee that you will NOT need them, and even if you did, there's nothing you can't buy in Orlando. As long as you have your phones, IDs, travel documents, and prescription medications, everything else is non-essential.
2 - Organize each piece of luggage with packing cubes, which will make unpacking and repacking a breeze, and allow you to maximize your use of the available space. Better yet, get each person packing cubes in their own color. If you want to maximize every inch in the cubes, roll your clothes, or use a folding board the same size as the cube (I custom-made one myself from cardboard and duct tape!), to fold everything neatly. Also, pack whole outfits together (shorts+shirt+undies+socks) in the order you intend to wear them, rather than organizing items by "type" (shirts in one cube, underwear in another), so you don't need to root around in multiple places to find what you want every morning. For toiletries, use Ziploc bags, fabric pouches, or a pack-it-flat-style toiletry kit, which can be laid on top of things easily, rather than bulky dopp kit style bags that aren't as easy to pack around.
3 - Don't bring anything the hotel will provide (e.g., soap, shampoo, hairdryer, tissues), unless you have a genuine need for a specific brand of something. Also, don't double up on items that the family can share: e.g., you don't need more than one tube of toothpaste, container of dental floss, or First Aid kit.
4 - Since your liquids and gels need to fit in 3-1-1 bags, decant sunscreen, moisturizers, etc. into smaller containers, or buy sample sizes. I even bring a tiny tube of cream deodorant, to avoid bringing a big full-size container. I sometimes use an upcoming trip as an excuse to pick up a Clinique or Estee Lauder "free with purchase" pouch of skin care/makeup samples. I also pack a travel-size folding hairbrush, since my everyday one is enormous.
5 - Wear all of your bulkiest items (e.g., sneakers, hoodie, hat if you're bringing one, pants if seasonally appropriate) on the plane. When choosing clothes to pack, opt for lightweight, breathable "tech" fabrics, which don't wrinkle, can be washed and dried in no time, and fold down into practically nothing. Wherever possible, pack items that can do "double duty" (e.g., a fitness dress that doubles as a pool cover-up).
Resist the urge to pack more outfits (or swimsuits, or PJs) than you absolutely need. Packing one extra shirt in case of a spill is okay: packing three extra outfits is not! DO NOT invest in "compression cubes," which are just in invitation to overpack, and to hurt yourself lugging around overly heavy luggage. Don't go overboard on footwear, which takes up a disproportionately large amount of space. A pair of sneakers (that you wear to travel), plus a sturdy pair of walking sandals that goes from the parks to the pool to dinner (e.g., Teva Tirra sandals in taupe or black), are plenty. Also, try to keep your traveling clothes and packed outfits in the same color family (e.g., black/gray, earth tones, red/white/blue, pink/teal/navy, so you can mix and match if and as needed.
6 - Make the most of your "personal items" for the plane. For yourself, bring a backpack or tote (depending on our destination and time of year, I bring a Baggallini Kindred tote, LL Bean Everyday Lightweight tote, or Eddie Bauer Stowaway backpack, that can double as our beach bag for the trip, and can be given to one of my kids to use as their "personal item" to hold souvenirs on the way home) that will fit under the seat. Your airline should specify the maximum dimensions for this. On your flight down, it can hold your purse/park bag (pre-packed with your wallet and phone, Band-Aids, tissues, Chapstick, sunglasses, MagicBands, rain poncho, etc.) plus breakfast foodstuffs, travel documents, chargers, additional electronics and earbuds, and other items you'll want for the journey -- and it will offer some extra "overflow" space in case your luggage fills up more quickly than expected. If you're still having trouble fitting everything in, outfit your spouse and teen with their own "personal item" backpacks, totes, or duffles (sized to fit under the seat in front of them) for overflow items.
7 - Consider bringing only half the clothes you need, and doing laundry in the middle of the week. We usually have a "pool afternoon" in the middle of a vacation anyway, and most laundry rooms are near the pools, so it's convenient. All you'll need is a "laundry kit" with a fabric laundry bag (or use the plastic laundry bag from your hotel room), and a sandwich bag with detergent sheets/powder pods, fabric softener sheets, and if needed, a few clothespins to line-dry fragile or delicate items. Disney sells these items in the laundry rooms, too, but we have some skin allergies in the family to some detergents, so we pack our own.
8 - When picking out luggage, keep in mind that rollaboards with 2 wheels (instead of the elevated roller bags with 4) offer a few extra inches of interior space, and that luggage that opens from the top like a trunk (rather than "clamshell" styles that open in the middle and get packed on both sides) can usually be packed with greater efficiency and flexibility.
*EXAMPLE: Here's what I packed for a 10-night trip to Scotland in the fall, during which I did visit an Inverness laundromat, although I was prepared to simply hand-wash and re-wear things: (1) a hobo tote for my "personal item" with everything I'd need on the plane; plus (2) a 22" wheeled carryon with packing cubes of clothes (5 pants, 6 long-sleeved tops, a smartwool sweater, long johns, underthings, socks, PJs), laundry and tote bags, slip-on shoes, etc., and an ebags "pack-it-flat" toiletry kit. For Orlando, I bring the same luggage and a slightly larger tote, and modify all of the contents to reflect the warmer destination -- which means I can pack for the full week with no laundry if I want to, since I'm just bringing lightweight shorts, breathable tops, and/or athletic dresses and rompers.
