I'd suggest ditching the flip flops and purchasing some water shoes before you go. You aren't allowed to have loose items that can be lost in the ride and if you don't have anyone waiting at the bottom of the rides to "hold" them for you--you're sunk. Same thing with sunglasses and hats. Don't plan on wearing them to the major rides unless they won't come off (ie. safety straps for the glasses). You hit some speed and turbulance on most of the rides/slides.
We saw people holding flip flops/watershoes on all the big slides- like Humunga Cowabunga. I held my camera on Slusher Gusher (2nd biggest slide at BB). I saw kids coming down Summit Plummit holding their lifejacket in their hands.
We never wear shoes around the parks- they always have water spraying on the sidewalks or we try to walk in the shade.
I don't wear flip flops at the water park either... I bought water shoes for the whole family and that's what we wear. I do wear my sunglasses, though, on all the rides...