It depends a little on the center, I think.
At mine, there were several copies of the key to the bathroom, and then you had a locker with a key (thank god it wasn't a combo lock!) where you could keep snacks, etc. Some people have said they could take a short walk outside, others said they weren't allowed to leave the center. There are lots of signs saying no reviewing notes, but I don't think it would have been hard to glance at a notecard in your locker before bio, if you were so inclined, not that I did, or that I advocate that sort of thing, all you prometric employees reading this 😀
Honestly, what with nerves, needing to be fingerprinted, signed in, and id'ed, all I did on breaks was grab a drink from my locker and go to the bathroom. I did finish a couple of sections early, and I used that time to "rest my eyes" because the freaking monitors suck, but I didn't walk away from the computer with the timer ticking, because I just couldn't do it -though I knew it would be okay, just couldnt.
