I bought a Camelback backpack (the one with the water pouch in it and the straw attached to the shoulder strap). I splurged and bought one with an additional large pocket and it worked great! I brought some pain medicine in a Ziploc bag, my contacts and glasses, rewetting drops, cell phone, and a book (larger than an average size paperback). The book was for when I was waiting in lines when I went off my byself (if you can, bring one, it really helps pass the time). Plus, the water pouch helped me stay hydrated. It was definitely worth it.
As for the rides, I just layed it on the floor and zipped up the head of the straw in the bag so it wouldn't touch the floors. It wasn't too big so I didn't have a problem.