I’ve invested more time and money in planning WDW packing than any other thing in my life.
What I’ve learned is: there’s so much you don’t need.
I love minimal packing, both on the plane and in the parks. For the majority of my trips I’ve had carry-on only on the flights. In the parks I’ve gone from a tote bag to a small washbag and, when I can, no bag at all.
In terms of packing, you need clothes and toiletries. Disney provides shower gel and shampoo. So I need my own toothpaste, toothbrush, sunscreen. I have to take antihistamines every day, so I bring those. And ibuprofen and antacid, just in case. Then there’s my phone, iPad and chargers.
The folks on here got me into packing cubes. I’m not 100% sure they’re necessary, but they do keep your suitcase very neat.
In the parks I carry a very light raincoat, that squishes up pretty small. I have sunglasses and regular glasses. My antihistamines. My phone, which has a battery case so it lasts all day. You can do everything with a Magic Band, so you don’t need a wallet, though some people take an emergency credit card, just in case Disney’s systems go down.
There are other things I’ve taken — a small fan, a cooling towel, a flannel, a blow-up cushion, a water bottle, a pair of Crocs for if it rains, spares socks — that I just haven’t used.
Depending on your budget, remember that Disney sells pretty much everything, and the health centres (or whatever they’re called) in each park are well-stocked. Ice cold water is free and readily available.
On my most recent trip I didn’t expect I’d be buying so many souvenirs and I ended up buying one of the new reusable Disney bags to carry them all in. The bag was maybe $2.
The one time I didn’t take my raincoat, it rained very heavily and I had to buy a Disney poncho, which was $12.