All you need to bring is two pieces of identification. You will not be allowed to bring anything into the exam room with you, so don't bother with scratch paper - they give you two sheets of laminated paper, a marker, and an eraser. They want to ensure you aren't cheating by bringing in anything you could have written on. An on-screen calculator is provided, the same one that is available on a PC - no scientific or graphing functions are available.
You will get one break of about fifteen minutes between the RC and Physics sections. Bring water and snacks for sure, but you won't be able to eat them during the exam, so use your break wisely to eat and use the bathroom. You can take unscheduled breaks during the exam, but the timer keeps going while you do, so I wouldn't recommend it.
This information is all on the website for the OAT and should have been in that ridiculously long document they make you read before registering for the exam, so I would also check that again.