We asked this question when we were preparing for our trip this summer and got lots of great suggestions. Someone suggested the Passporter pass holder (
www.passporter.com) and I ordered that. It was worth its weight in gold at the parks! It easily held our Hoppers, room key, ID, cash, Fastpasses, etc. I wore it around my neck our whole trip and really hated having to go back to carrying my big old purse when we got home.
Drawbacks--the thing didn't seem very waterproof; I think they
said it's water resistant but to cover it up if it's really
raining (and it's not good for waterparks; you need
a genuinely waterproof one for that). We were
caught in a rainstorm and didn't have trouble
with the contents getting damp, however.
---Also, it's not exactly a "cool" thing to wear IMO. It's
very brightly colored, with bright printing on the
front. I wore it backwards (with the printing to
the inside) because I felt like a walking
Passporter ad otherwise!