For the floats, if you arrive a little later in the day (like after 11am, you will start finding lots of "abandoned" floats. We just watched a few floats for a while, asked a few people who were sitting around the floats if those were theirs, and if not, we used them!
Don't worry if the glass bottom boat is full, it isn't very fun. Old dirty boat, we only saw a few schools of fish, and we had to stand the whole time. A big waste of $25 per person (now I think it is $35)