So, I have a couple weird things that I bring... I'm a packing and gear nerd:
I love my Sitka over-the-shoulder sling bag from Maxpedition. It is designed so that when you go to sit down, or access the bag for that matter, that it slides to your front and sits across your abdomen-perfect for riding rides and great for getting at stuff without taking the bag off! It is not terrible large, but you can pack enough in there if you don't go too crazy. Besides, if you pack too much, it will be too heavy for one shoulder anyway. (Ladies, if you want to get your DH to carry stuff, this might be a great bribe-looks cool, works great, very manly...

)
I keep a "dry sack" in my bag because Florida rains are notorious for popping up out of nowhere! My "dry sack" is big enough to hold my Sitka inside it, so when rain happens, I step inside somewhere dry, pull my dry sack out, and drop my whole backpack in there, and voila!, we keep going and ride those rides with short lines while everyone is hiding from a little rain!
I have a MSR Paktowel Original in my bag. These things are amazing. They hold almost 10x their weight in water. Wring it out, and it's almost completely dry again. Great for wiping down wet seats, drying off somewhat from rides or spray... Lots of uses...
I never leave my Unofficial Guide behind (or my iphone with my Lines app and My Disney Experience on it!)
I have a portable (battery-operated) charger so that we can recharge our phones while we eat lunch/dinner. It is great. It's about half the size of my UG, and will fully recharge my phone battery from 30% to full in about an hour.
I bring a Camelbak bladder that fits inside my Sitka (that also has a bladder compartment made for it). The low profile Omega fits perfectly (and holds 3L). Fill it up with ice and water/lemonade/crystal light, and it keeps your back cool and gets lighter the more that you drink!
I bring a surgical tube clothesline that I got from
Amazon (It's braided with three tubes, so no need for clothespins). It has loops on either end. You can attach carabiners to them or loop them around shower heads. It's only 7 ft long, but great for what it does, and it stretches a bit longer.
I put luggage tags on all my bags, especially the one I bring into the park. Disney customer service is awesome, and they will return something if they can figure out who it belongs to!
I think that's all that may not have been said already (and sorry for anything that's already been posted!). Thanks for all the tips! I'm a huge fan already!