Depends on the subject.
For essay subjects I'd go over last minute notes/diagrams (although I'm really talking about in the morning before the exam), but for something like maths all I'd do would be to check my trigonometric equations, that I know how to calculate the mean/standard deviation/etc quickly on my calculator and leave it at that. I wouldn't be doing any 'proper' revision by that stage.
Honestly, just relax. I tried cramming in before a business exam and by the time I got in the exam room all I could remember was the last thing I looked at. I ended up writing my full essay on the things I had revised that morning, instead of the entire unit which I had spent a year learning.
Revise (or you might regret it later) but ideally you will be fully prepared by that point, so it should be just going over stuff, then give yourself time to relax too, spend time with your family etc. You won't take in much that day but it will give you reassurance you have done a bit of revision the day before.