A Singaporean Airline some time ago, perhaps still, used to have on the before start checklist;
"Lap top power cords. CM1..on board..CM2.. on board"
Arghhh..
Why not put 'seat belt fastened" on that checklist and "shoulder straps fastened' for good measure.
This is right up there with "talking the instruments" on the ground in a glass cockpit.
Any change to the checklist normally has to be sanctioned by the manufacturer in the form of a no technical objection letter. Failure to due so risks liability in the event of an incident/accident.
A fairly new 744 Cargo Airline had a Chief Pilot who had only flown 737s. He decided that he would change the after takeoff checklist to "Flaps up.. no lights". When it was pointed out to him that it doesn't have 'lights' and that Boeing really likes you to talk to them before changing tha checklist he got all red faced.
Take a look at the Boeing standard before takeoff checklist for 744. "Flaps..."
Hard to fcuk that up. Have a look around the cockpit at everything that might suggest you have the correct flaps, pause meaningfully, and respond.
If you have left your mobile on, ignore it...