When I was living in Florida (I worked at Disney for a year), I basically lived in flip flops when I wasn't at work. When I head back now, I still have the same pair of flip flops, but I also have walking sandals that I've owned for years. Because I have a thing for Little Miss Matched socks, I will actually wear them with my sandals if it gets chilly (by FL standards, I mean)... however they are always knee high socks, never ankle ones. Or I just wear them with my tights (I pretty much only wear skirts).
As for rides with flip flops, if it's a ride where the feet are dangling free, I like to have bare feet to feel the breeze, so I either leave my flip flops at the loading dock, where possible, or slip them on my hands.