Dont need a cage to do a trackday. You need a helmet and your driving license.
Passenger usually have to pay a small fee (a tenner)
Thats pretty much it.
Small tool kit and gaffa tape (you would be suprised what that can fix lol), oil, petrol can maybe.
Just prep your car before you go (oil, tyre condition, brakepad life) and enjoy the day, who wants to be bonnet up between outings all day

Go on an open pitlane trackday, sessions are pony

http://www.easytrack.co.uk/article/track_day_cars