What to expect at an exit interview?

Skip it. If they didn't care about your opinions when you worked there, why should you give them free advice on the way out?

you dont

They'll ask you questions about if you liked it or not, and would you recommend them to others, do you have any questions about your pension contributions, have you got any equipment to hand back.... It's a good idea to be positive about it if it's a company that you could end up working for again, for example if you work somewhere else and then the company you gave the exit interview with takes over a contract, you would be looking at transferring back and the notes of the exit interview would be the first thing they get out. You don't really have to go to an exit interview at all, but I would go and be nice. Not a lot of places do it, I've had one exit interview in the last 18 or so years I've been working.