Question about exams

I get this may seem daft, but are there rules about what we can wear in exams? When I was in year 11, we had an exam on our last day of school, and the teachers checked that we didn't have our decorated shirts on for the exam (this included taking our jumpers off so teachers could properly see the shirts underneath), and I'm assuming they did this since they would have had writing on which could have been used to cheat. However, in college, there obviously isn't a uniform, meaning we can wear whatever we want, but clothes have writing on them. Is there anything I should or should avoid wearing?

ALSO, are there rules about the water bottle you can take in to the exam. I know they have to be clear, but I've heard that they apparently have to be ones where you pull the lid up or you pull the straw up, so that way water won't get everywhere if it gets knocked over. Is this true?