Keep in mind that there is a weight and size limit on carry-on luggage (although not strictly enforced most times)
I got caught once with a very overstuffed carry-on on our way home (no checked bag and a couple or 8 too many souvenirs). I was at almost 30 pounds and had to pull out 5 pounds of misc stuff (right at the check-in counter) and spread it out between my wifes carry-on and our 2 personal items.
If your just taking a carry-on I would suggest looking for one of those Ultra Lite ones, a lighter case means you can cram more stuff in and not be over the weight limit.
The following is my week or less, carry-ons only packing strategy for Florida during most of the year (Winter may require an extra pair of jeans for cool days/evenings):
1)have a rough idea of what you will do and where you will be each day and plan the wardrobe accordingly (ie park days, a day at the beach, ADR's etc).
2)Pack light and minimally Your heaviest stuff can usually be worn on the plane ie: jeans, jacket/hoodie, dress shoes,boots or runners.
3)The one long pair of pants or jeans that you may need for a cool evening or for a night out, should be worn on the plane, then hung in the closet to "de-wrinkle" when you arrive at your resort (or spot cleaned if needed- I always managed to get a splash of coffee or some jelly from my danish on my pants no matter how careful I am)
4)Shorts can usually be worn for more than one day, so 4 pairs for a week would be fine. For your 5 day excursion 3 pairs should do it.
5)Shirts, personally I need a clean one each day (sometimes my DW can stretch a little) plus one for the flight home. This would be 6 for a 5 day trip unless you plan to buy and wear a couple of souvenir shirts (keep in mind, they will still have to fit in the carry-on on your way home even if you didn't take them with you)Cotton shirts feel nice but can be heavy and add bulk to you bag, consider a light summer blend material for maximum comfort and to help with the packing.
6)Socks and undies are pretty light and easy to pack. A pair per day plus an extra for the trip home. ***if you are going in the summer, a couple of extra pairs may come in handy due to the heat/sweat and don't really take up a whole lot of extra room
7)A second nice light and COMFY pair or shoes for all those miles in the parks.
8)as you are not taking a checked bag, make sure to get travel size toiletries so you can get through TSA without issue.
9)Don't forget a bathing suit.
10)Take a couple of those laundry sheets(detergent and fabric softener in one) or a couple of the Tide Pods (in your 3-2-1 bag) with you just in case there is a mishap or miscalculation with the clothing. Then you can do a load of laundry at your hotel. NOT usually needed for less than a week except for emergencies but a must if you are trying to do 7 days+ with carry-ons and personal items only
11)use all available space, so fill your extra pair of shoes with the socks you are taking. Rolling shirts and undies seems to take up less space for some reason and shirts come out less wrinkled.
12)instead of starting at the bottom and layering in pants then shirts, then undies, I like to pack in different sections of the case. All shorts together, all shirts together etc. , then if I need a new pair of shorts I don't have to go digging down to the bottom of the case, underneath everything. It keeps the case neater and easier to find stuff. I believe this is why people like to use packing cubes, keeps everything separated.
Lastly, get one of those portable travel scales to weigh you bags, as I said at the beginning there is a weight and size limit, most airlines allow 20-25lbs.
