I have tried every bag out there. My favorite is a messenger bag from Old Navy. It is waterproof and has a zipper on the bottom to make it wider. I carry poncho, small umbrella sometimes, wallet, cell phone, camera, small bag with chapstick, etc and a brush. Still have room for a few other things..even got Pal Mickey in there when it was unzipped one rainy night! It is compact and lightweight. Can even fit a water bottle in there. My daughters each carry one as well with their poncho, autograph book, gum, mouse ear headbands, pin lanyards and if we will be out at night any light up spinning toys they want. Can still get a lightweight sweatshirt in it.
Best bag ever!