Like others, on our most recent visit there was no problem with small backpacks or shoulder bags as most rides (at least the ones we went on) had special bins for those bags right on the ride. Moleskin was a life as well as vacation saver! I like the idea of the filtered water bottles (I wish we'd had them).
The check of bags at the gate was cursory, I slipped my Spyderco Yojimbo into my pocket so the tell-tale clip wasn't visible. No worries there.
Light plastic rain poncho's are a must for summer travel to the park (it rains most afternoons). We got a bunch at Wal-mart and Gander Mountain when they were on sale for around $1 a piece. We carried at least two at a time per person. When the rain appeared over we ditched them in the trash bins as refolding them was a pain (especially if wet).
One other thing, like was mentioned before, PLAN! My wife (bless her heart) planned our days around meal times and we always stopped for dinner around 4-5 pm (which usually coincided with the afternoon rain shower) which got us in to eat before others were ready, and back into the park when all the eating venues were full and the attractions were less crowded.
We stayed in the Sports complex and while the rooms were not anything special, they are private and comfortable and all you need since the PARK is the attraction. Also the pools stayed open until Midnight or 1 am which was nice after a long day.
Have fun!