When we went in Janaury I bought fanny packs for myself, my adult son, and my 8 y/o GD. They refused to wear theirs. I had bought Disney t-shirts for the characters to autograph for my GD and they wouldn't both fit in my fanny pack, so I wound up buying one of those small Disney backpacks while I was down there. It was cute, small, light, and worked well (held camera, cell phone, water bottles, both t-shirts, sun screen, lip balm, and mini first aid kit).
I'm going back solo in May and plan to take that Disney backpack, my Lewis N. Clark fanny pack (which has a strap, so it can be worn across the body as a messenger bag, as well as a fanny pack), and a really cute very small (8"x9") multipocketed messenger bag I just won on E-bay, that is made to be worn across the body. Both the Lorenz messenger bag and the fanny pack have lots of pockets. I'll only be taking one of them into the park each day of course, but will be able to decide down there which works better (fanny pack, messenger bag, or small back pack). I also just bought one of those insulated bottle carriers from Nutztogo that will either go around my neck or else in the backpack. It has a small (4"x5") zippered compartment on it that looks like it will hold tickets, ID, room key, and a little cash, so I may just use it some days. The neck strap is detachable and it has little double straps on the back that can thread onto a fanny pack strap.