When DH and I travel, I have a several types of day bags that I can easily pack flat in the carryon. Normally I bring 2 different sizes, I have a fold up one that can fit in DH cargo shorts pocket, when its unfolded it will hold quite a bit and has long straps so you can use it over the shoulder, and a more canvas style with adjustable straps for if we are going to be away all day from the resort, or we use it pool side, to hold towels, cover-ups, snacks, glasses, and phones. I use a small cross-body Dooney and Burke for all my personal items. See the list below.
DH and I are empty nesters, and are AP and Fl. residents so we visit a lot... I use a small Disney Dooney and Burke cross-body purse...I have a small wallet, glass case, phone, foldable brush with a hair band wrapped around the handle, a small zippered medicine pack (4X3) - that holds a couple of band aids, tummy pills, pain reliever, alcohol wipes, and a few allergy pills. Hand sanitizer clipped on the strap, some hard candy, a couple of cough drops.
If the whole family is with us, there is a back pack full of stuff... Snacks, water bottles, extra complete outfits for the grandkids (2 outfits)... depending on the age maybe more, including a pair of shoes and a couple pairs of socks. Rain jackets, anti bacterial wipes, small hand towel, hand wipes, and Kleenex. Sun Screen, hats, and something to keep them busy at the table during meal time, and some type of small toys for when we are in line, that can be tucked in a pocket quickly. Light weight blanket depending on the time of year. We take in a stroller so we have somewhere to put it.
When our DD's were little, I used a list to repack the bag every night for the next day, this way stuff did not get left in the room... DH would go back over it in the morning, and when the DD's got older they would help and double check the list. Also I found out that getting sun screen on the kids was easier in the room and let it soak in, instead of fighting with them in the parks...