I bought a drawstring backpack from Disney. It's heavier material,and has a small zip pocket that fits my Samsung S8 phone, and it has seen some "stuff" in its day. I had my friend buy a replacement but I have yet to use the replacement one. It's a dingy rainbow checker, but it's my absolute favorite.
I usually purchase, refill, and recycle a 20oz Dasani bottle when I get to the parks. In addition to that, I have a wallet or a smaller purse holding small items inside.
I usually have hand sanitizer, sunscreen, my phone, travel wipes, and my sunglasses case inside. The purse I use is about 9"x7"x2" rectangular. I usually use it to hold my wallet, cards, hand sanitizer, lip balm, etc. I also have a hat that I can bend flat and stuff into the purse.
I know it sounds stuffed, but it isn't terrible.
I like the backpack because it evenly distributes weight on my back and shoulders instead of concentrating it on my shoulder or hip.