Here's a few ideas I had at the beginning of this thread on some easy costumes.
Quick, easy to pack costumes.
101 Dalmations...White shorts/pants and t-shirts and go to town with spots! Ears could be made out of felt or craft foam on ball caps (esp for the guys) or maybe headbands for the ladies.
Mickey Mouse Club...Red pants,mouse ears,t-shirts with each ones name on it.

Baseball players...Your favorite team's jersey/t-shirt and a ball cap,shorts or sweats and sneakers.
Hippies...Tye dyed shirt,round framed glasses,beads,peace sign jewlery,jeans or a long skirt and sandals.
Pirate... Easy and light weight too.Black shorts or capris,striped shirt,bandana,an eye patch,a hoop earring and there ya go....arrrrrrrrrrgh matey!
MrsJackSparrow...you won't feel left out either way you go! There are alot of adults not in costume ,some just wearing Halloween shirts or colors or your normal "I'm at WDW" clothes! !.
I am LOVING hearing about everyone's costumes! We won't have DSS Jon this year but DS Erich wants to be Legolas (sp?) from Lord of the Rings. I keep telling him a wig will be soooo hot in Florida! I'm not sure if or what Joe and I will wear.