News of the evacuation of a British Airways a/c at Phoenix shortly after push back from the terminal reminded my why safety considerations are important even at the start of the flight.
I always keep my footwear on until well airborne. Those without footwear would have had a hard time walking across the tarmac in temperatures well over 100F.
I keep my wallet, passport & glasses on me. There may not have been time to retrieve these if they'd been stowed away. Not having these for hours or a day until carry-ons given back by the airline would have been very inconvenient.
I admit I'm not always that alert at the start of a flight, particularly for an evening departure of an overnight flight as this one was.