So excited that our first trip to Universal is almost here! I am wondering whether you need to wear shoes with backs on them. I have good walking sandals that are slip-ons and dd is addicted to flip flops and will want to wear them sometimes even if I usually try to get her to wear sneakers. Are flip flops a no-no for any ride, and if so does it mean you can't ride or that you have to leave them like you would on Soarin? Thanks!