Interesting observation at Disney. I visited the one in Florida and to the best I can recall went the hiker style with a much smaller pack. Coming from an arid region I always carry water. Coming from an outdoorsman background I carry snacks, first-aid, and anticipated clothing needs rather than be uncomfortable or someone's dependent. I also carry a monopod/walking staff for photography and back pain relief. You are quite right that we dress partially due to background.

Regarding fly fishing, I often wade shallow streams in river sandals and Utilikilt. I've been photographed by curious passerby and always feel quite comfortable in the hot dry Colorado sun.