“Put some thought into it” is a little insensitive...those of us who are disabled and/or neurodiverse require a little more than pockets will carry sometimes. Like when you’re chronically ill and have to carry a whole bunch of meds and can’t subsist on tiny free cups of ice water from QS locations. And Gods help you if Aunt Flo pays a visit and you need to carry those supplies (that happened to me on a trip and it sucked!). My gf brings a set of noise canceling Bose cans to drown out ambient noise during times she’s feeling overstimulated and it’s the only way she can enjoy fireworks.
There are plenty of legitimate reasons why childless adults need to carry backpacks into the parks. It’s easy to assume everyone has your circumstances, but not everyone does. Everyone is different and has different needs.
Well, let's consider your list: A "whole bunch of meds" can be packaged quite small for day-use (and by carrying only the pills you're likely to need THAT DAY, you don't risk losing larger bottles). You can order two "tiny" cups of water or specify that you'd like a large cup. A couple tampons take some space (I used a Diva Cup for the last decade + that I needed such supplies, and I loved not needing to carry supplies /only needing to change first thing in the morning, once in the afternoon, once at bedtime). A waterbottle and headphones do take some space, but all -- and more -- that will fit in a mini-backpack (or a sling pack is about the same quantity).
A daypack is pretty big, and it's not necessary for the things you've listed. Also, a person with a chronic illness is certainly going to have a better day in the parks if they don't load themselves down with a bunch of stuff.
We have older children, but still found the backpack useful for carrying a couple bottles of water, sanitizing wipes, and hand sanitizer. I also have a larger cell phone, which doesn't fit in my pocket. Additionally, I found it helpful to bring a portable cell charger, because using the app and taking photos, the battery goes quick. For photos, you can set the backpack down.
Again, the things you mention don't require a whole day pack.
How are people getting by with just a pocket during an entire day at a park? I must be doing it wrong... usually I take;
Advil, cell, sanitizer, Bandaids, poncho and even have taken a batt bank (and now extra masks).
I only go to Disney during warm months, and I tend to wear one of two things:
- A casual dress with bicycle shorts underneath. The bicycle shorts have a big pocket on each leg -- my large phone fits easily into one. With a hat and prescription sunglasses.
- Shorts with lots of pockets and a blouse-y top. I wear a women's small in shorts, and my large phone fits in my back pocket. Again, with a hat and prescription sunglasses.
The for-sure things I carry in pockets are: my (large) phone, a couple Neospirin-infused bandaids, and a little ziplock with my ID, tickets, money.
I might carry a point-and-shoot camera, and IF the weather looks to be bad I will carry a disposable poncho (if a quick afternoon shower is expected, I'm more likely to sit down in a restaurant for a drink and a snack, or go into an indoor attraction). I wash my hands in restrooms, and since I don't play on my phone my battery will last a whole day.
Going "light" is very freeing, and I highly recommend it.