Master - because you may not have the alternator/generator selected. Better to find out now than when trying to restart.
Mags - checking they are both on.
Hatches & Harnesses - making sure everyone is belted in and the ship is secure.
Fuel - making sure your selector is on the main tank, both or the fullest depending on the type you are flying. You would cry when you see the amount of accidents from PA31s and fuel starvation issues landing on outer wing tanks.
Undercarriage - I used to check the tyre making sure it was inflated etc. because I always checked, I never had a gear up landing. I bet the guys who think its a waste of time in a non retractable aircraft will go back to prelearned behaviour under pressure and have a gear up landing.
Anyway, do what your instructor, chief pilot, check captain says. It's their train set and when you get to make the rules, you can get people to play with it as you see fit.