transit – 6 hours at the airport: what should I do without leaving the airport? (OR Tambo, South Africa)

I have a flight arriving at 3pm in Johannesburg, OR Tambo. My flight leaves the next day at 9am, so I sleep at the airport. I have about 6 hours, I think to be awake, what should I do to stay busy? I do not have a visa, which means that I can not leave the airport, but I can go to the boarding gates and so on. my boarding cards, check-in etc.