I haven't ever been there on Opening Day, but from what I've read and temps predicted in the 70's, I'd say it's going to be crazy busy. I'm assuming refillable mugs are still in effect since I haven't read anything differently, so I'm hoping someone else will have some info on that one, also. My advice is to get there early!! If I had the chance to go Opening Day, would I go? You bet! Crowd predictions wouldn't keep me away, so if you go, have a great time, and give us a review.