Rain in WDW is a variable experience. While nothing is etched in stone, summer rain tends to be heaver than winter rain. In summer I wear fully waterproof quality sandals. In winter, I can usually get away with sneakers, and they don't get soaked.
I've tried almost everything:
Crocs sometimes have an odd way of catching on the pavement that can lead to tripping.
Cheap flip flops can get very slippery on the inside, but if you are bringing a day bag, then they fit easily as an short term option while the rain is heavy. They are pretty light and compact.
Other times, in the past, we've been able to simply wait out the downbursts. (Harder to do now with fixed FP times.)
The big thing with wet sneakers is that they can develop a very foul odor!
If all else fails, there's an outlet mall near WDW! (just across I-4)