Guiding principle: Less is more.
You are paying to be at a monorail resort, if you get wet get on the monorail and go change. Don't lug around a change of clothes! As OP stated I too use a fanny pack, cinched in the rear so my bag is always accessible to me and not pick pockets. You can get a single koozie that clips on to hold a water bottle. Its only you and your daughter, so travel size things will work well. There are first aid kit/packs sold maybe 5 in a box and one will easily fit in a fanny pack. Ponchos, those I think are a must $1 at the dollar store at home. Bring one per day, but buy a couple extra. That way if you decide to pitch one you have a back up at the hotel. Consider a bandana vs a towel, lighter and still useful to blot your self dry. Also can be tied to a beltloop for easy carrying.
My fanny pack holds: digital camera, hotel key, ID, credit card(just one), discount card like
AAA if it matters, cash, hand sanitizer, poncho, sunglasses, first aid items, lip balm, small sun screen stick/tube, cell phone
My water strategy is to drink lots before arriving at the park ie. carry inside my body. I will likely still get some kind of drink during my visit, but most will be had beforehand. I'm the one downing a bottle before airport security or entering the arena! You can do the same when you take a hotel break from the park, load up then sip your way through.
Have a great time!